Artificial entropic bristle domain sequences and their use in recombinant protein production

ABSTRACT

Compositions and methods for recombinant protein production and, more particularly, fusion polypeptides, polynucleotides encoding fusion polypeptides, expression vectors, kits, and related methods for recombinant protein production.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/886,280, filed Sep. 20, 2010, which is a continuation-in-part of U.S.patent application Ser. No. 12/272,558, filed Nov. 17, 2008, whichapplication claims the benefit under 35 U.S.C. §119(e) of U.S.Provisional Patent Application No. 60/988,319, filed Nov. 15, 2007;where these applications are incorporated herein by reference in theirentireties.

STATEMENT REGARDING SEQUENCE LISTING

The Sequence Listing associated with this application is provided intext format in lieu of a paper copy, and is hereby incorporated byreference into the specification. The name of the text file containingthe Sequence Listing is 670098_(—)406C3_SEQUENCE_LISTING.txt. The textfile is 173 KB, was created on Dec. 13, 2011 and is being submittedelectronically via EFS-Web, concurrent with the filing of thespecification.

FIELD OF THE INVENTION

The present invention relates generally to compositions and methods forimproved recombinant protein production and, more particularly, tofusion polypeptides, polynucleotides encoding fusion polypeptides,expression vectors, kits, and related methods for recombinant proteinproduction.

DETAILED DESCRIPTION OF THE RELATED ART

A large percentage of the proteins identified via the different genomesequencing effort have been difficult to express and/or purify asrecombinant proteins using standard methods. For example, a trial studyusing Methanobacterium thermoautotrophicum as a model system identifieda number of problems associated with high throughput structuredetermination (Christendat et al., (2000) Prog. Biophys. Mol. Biol.73(5): 339-345; Christendat et al. (2000) Nat Struct Biol 7(10):903-909). The complete list of genome-encoded proteins was filtered toremove proteins with predicted transmembrane regions or homologues toknown structures. When these filtered proteins were taken through thecloning, expression, and structural determination steps of a highthroughput process, only about 50% of the selected proteins could bepurified in a state suitable for structural studies, with roughly 45% oflarge expressed proteins and 30% of small expressed proteins failing dueto insolubility. The study concluded that considerable effort must beinvested in improving the attrition rate due to proteins with poorexpression levels and unfavorable biophysical properties. (Christendatet al. (2000) Prog. Biophys. Mol. Biol. 73(5): 339-345; Christendat etal. (2000) Nat Struct Biol 7(10): 903-909).

Similar results have been observed for other prokaryotic proteomes. Onestudy reported the successful cloning and attempted expression of 1376(73%) of the predicted 1877 genes of the Thermotoga maritima proteome.However, crystallization conditions were able to be determined for only432 proteins (23%). A significant component of the decrease between thecloned and crystallized success levels was due to poor proteinsolubility and stability (Kuhn et al. (2002) Proteins 49(1): 142-5).

Similarly low success rates have been reported for eukaryotic proteomes.A study of a sample set of human proteins, for example, reported thatthe failure rate using high-throughput methods for three classes ofproteins based on cellular location was 50% for soluble proteins, 70%for extracellular proteins, and more than 80% for membrane proteins(Braun et al. (2002) Proc Natl Acad Sci USA 99(5): 2654-9).

Interactions between individual recombinant proteins are responsible fora significant number of the previously mentioned failures. In ahigh-throughput structural determination study, Christendat andcolleagues found that 24 of 32 proteins that were classified by nuclearmagnetic resonance as aggregated displayed circular dichroism spectraconsistent with stable folded proteins, suggesting that these proteinswere folded properly but aggregated due to surface interactions(Christendat et al. (2000) Prog. Biophys. Mol. Biol. 73(5): 339-345).One possible explanation for this is that these proteins function invivo as part of multimeric units but when they are recombinantlyexpressed, dimerization domains are exposed that mediate protein-proteininteractions.

Prior methods used to increase recombinant protein stability includeproduction in E. coli strains that are deficient in proteases (Gottesmanand Zipser (1978) J Bacteriol 133(2): 844-51) and production of fusionsof bacterial protein fragments to a recombinant polypeptide/protein ofinterest (Itakura et al., Science, 1977. 198:1056-63; Shen, Proc NatlAcad Sci USA, 1984. 81:4627-31). It has also been attempted to stabilizeforeign proteins in E. coli. In addition, fusing a leader sequence to arecombinant protein may cause a gene product to accumulate in theperiplasm or be excreted, which may result in increased recovery ofproperly folded soluble protein (Nilsson et al., EMBO J, 1985.4:1075-80; Abrahmsen et al., Nucleic Acids Res, 1986. 14:7487-500).These strategies have advantages for some proteins but they generally donot succeed when used, for example, with membrane proteins or proteinscapable of strong protein-protein interactions.

Fusion polypeptides have also been used as an approach for improving thesolubility and folding of recombinant polypeptides/proteins produced inE. coli (Zhan et al., Gene, 2001. 281:1-9). Some commonly used fusionpartners which have been linked to heterologous protein sequences ofinterest include calmodulin-binding peptide (CBP) (Vaillancourt et al.,Biotechniques, 1997. 22:451-3), glutathione-S-transferase (GST) (Smith,Methods Enzymol, 2000. 326:254-70), thioredoxin (TRX) (MartinHammarström et al., Protein Science, 2002. 11:313-321), andmaltose-binding protein (MBP) (Sachdev et al., Methods Enzymol, 2000.326:312-21). Glutathione-S-transferase and maltose-binding protein havebeen found to increase the recombinant protein purification success ratewhen fused to a heterologous sequence in a controlled trial of 32 humantest proteins (Braun et al., Proc Natl Acad Sci USA, 2002. 99:2654-9).Further, maltose-binding protein domain fusions have been shown toincrease the solubility of recombinant proteins (Kapust et al., ProteinSci, 1999. 8:1668-74; Braun et al., Proc Natl Acad Sci USA, 2002.99:2654-9; Martin Hammarström et al., Protein Science, 2002.11:313-321). Maltose-binding protein may further benefit recombinantprotein solubility and folding in that it may have chaperone-likeproperties that assist in folding of the fusion partner (Richarme etal., J Biol Chem, 1997. 272:15607-12; Bach et al., J Mol Biol, 2001.312:79-93. However, these fusion approaches used to date have not beenamendable to all classes of proteins, and have thus met with onlylimited success.

Entropic bristles have been used in a variety of polymers to reduceaggregation of small particles such as latex particles in paints and tostabilize a wide variety of other colloidal products (Hoh, Proteins,1998. 32:223-228). Entropic bristles generally comprise amino acidresidues that do not have a tendency to form secondary structure and inthe process of random motion about their attachment points sweep out asignificant region in space and entropically exclude other molecules bytheir random motion (Hoh, Proteins, 1998. 32:223-228). Entropic bristlesare singular elements, comprising highly flexible, non-aggregatingpolymer chains, of which entropic brushes are assembled. In polymerchemistry, entropic bristles have been affixed to the surfaces ofparticles (e.g. latex beads), thereby forming entropic brushes which, inturn, prevent particle aggregation (Stabilization by attached polymersteric stabilization, in Polymeric stabilization of colloidaldispersions, D. H. Napper, Editor. 1983, Academic Press: London. p.18-30). EBDs can exclude large molecules but do not exclude smallmolecules such as water, salts, metal ions, or cofactors (Hoh, Proteins,1998. 32:223-228).

EBDs can also function as steric stabilizers and operate through sterichindrance stabilization (Stabilization by attached polymer: stericstabilization, in Polymeric stabilization of colloidal dispersions, D.H. Napper, Editor. 1983, Academic Press: London. p. 18-30). Naperdescribed characteristics that contribute to steric stabilizationfunctions, including (1) they have an amphipathic sequence; (2) they areattached to the colloidal particle by one end rather than being totallyadsorbed; (3) they are soluble in the medium used; (4) they are mutuallyrepulsive; (5) they are thermodynamically stable; and (6) they exhibitstabilizing ability in proportion to their length. Steric stabilizersintended to function in aqueous media extend from the surface ofcolloidal molecules thus transforming their surfaces from hydrophobic tohydrophilic. The fact that sterically stabilized particles arethermodynamically stable leads them to spontaneously re-disperse whendried residue is reintroduced to solvent. Entropic bristles can adoptrandom-walk configurations in solution (Milner, Science, 1991.251:905-914). These chains extend from an attachment point because oftheir affinity for the solvent. This affinity is due in part to thehighly charged nature of the entropic bristle sequence.

While naturally-occurring EBDs possess features desirable for use inimproving the solubility, folding, etc., of recombinant proteins, priorattempts at using EBD sequences in fusion with heterologous proteinsequences have met with limited success, due in part to cellulartoxicity associated with the naturally occurring EBDs. Accordingly,there remains a need for new compositions and methods for improving theproperties and characteristics of recombinant proteins, e.g., improvingsolubility, stability, yield and/or folding of recombinant proteins. Thepresent invention addresses these needs and offers other relatedadvantages by providing non-naturally occurring EBD sequences as fusionpartners for use in recombinant protein production techniques, asdescribed herein.

SUMMARY OF THE INVENTION

According to a general aspect of the present invention, there areprovided isolated fusion polypeptides comprising at least oneartificial, non-naturally occurring entropic bristle domain (EBD)sequence and at least one heterologous polypeptide sequence of interest.The fusion polypeptides comprising artificial EBD sequences as describedherein offer a number of advantages over prior fusion polypeptides andmethods relating thereto. For example, the fusion polypeptides of theinvention offer increased solubility relative to the heterologouspolypeptide sequence, reduced aggregation relative to the heterologouspolypeptide sequence and/or improved folding relative to theheterologous polypeptide sequence.

In one illustrative embodiment, the invention provides fusionpolypeptides comprising at least one non-naturally occurring entropicbristle domain (EBD) polypeptide sequence and at least one heterologouspolypeptide sequence to be expressed, wherein the EBD polypeptidesequence is about 10-1000 amino acid residues in length, and wherein atleast 75% of the residues of the EBD polypeptide sequence are selectedfrom G, D, M, K, R, S, Q, P, and E. In other embodiments, at least 80,85, 90 or 95% of the residues of the EBD polypeptide sequence areselected from G, D, M, K, R, S, Q, P, and E.

In another illustrative embodiment, the EBD polypeptide sequence ispositively charged and the amino acid residues which make up the EBDpolypeptide comprise disorder-promoting amino acid residues selectedfrom P, Q, S and K. In a more specific embodiment, thedisorder-promoting amino acid residues P, Q, S and K are present inabout the following amino acid ratios: K:P:Q:S=1:2:1:1, K:P:Q:S=1:4:1:1,K:P:Q:S=2:2:1:1, K:P:Q:S=3:2:1:1, K:P:Q:S=1:2:1:2, K:P:Q:S=2:2:1:2,K:P:Q:S=3:2:1:2, K:P:Q:S=4:2:1:2, or K:P:Q:S=5:2:1:2. In a more specificembodiment, the EDB polypeptide sequence comprises a sequence set forthin SEQ ID NO: 1, SEQ ID NO: 2, SEQ ID NO: 3, SEQ ID NO: 4, SEQ ID NO: 5,SEQ ID NO: 23, or SEQ ID NO: 24, or a fragment thereof, or a sequencehaving at least 90% identity thereto.

In another illustrative embodiment, the EBD polypeptide sequence isnegatively charged and the amino acid residues are disorder-promotingamino acid residues selected from P, Q, S and E. In a more specificembodiment, the disorder-promoting amino acid residues P, Q, S and E arepresent in about the following amino acid ratios: E:P:Q:S=1:2:1:1,E:P:Q:S=1:4:1:1, E:P:Q:S=2:2:1:1, E:P:Q:S=3:2:1:1, E:P:Q:S=1:2:1:2,E:P:Q:S=2:2:1:2, E:P:Q:S=3:2:1:2, E:P:Q:S=4:2:1:2, or E:P:Q:S=5:2:1:2.In a more specific embodiment, the EDB polypeptide comprises thesequence set forth in SEQ ID NO: 6, SEQ ID NO: 7, SEQ ID NO: 8, SEQ IDNO: 9, SEQ ID NO: 10, SEQ ID NO: 25, SEQ ID NO: 26, SEQ ID NO: 38, SEQID NO: 39, SEQ ID NO: 40, or a fragment thereof, or a sequence having atleast 90% identity thereto.

In another illustrative embodiment, the EBD polypeptide sequence isnegatively charged and the amino acid residues are disorder-promotingamino acid residues selected from P, Q, G and E. In a more specificembodiment, the disorder-promoting amino acid residues P, Q, G and E arepresent in about the following amino acid ratios: E:P:Q:G=1:2:1:1,E:P:Q:G=1:4:1:1, E:P:Q:G=2:2:1:1, E:P:Q:G=3:2:1:1, E:P:Q:G=1:2:1:2,E:P:Q:G=2:2:1:2, E:P:Q:G=3:2:1:2, E:P:Q:G=4:2:1:2, or E:P:Q:G=5:2:1:2.In a more specific embodiment, the EDB polypeptide comprises thesequence set forth in SEQ ID NO: 41, SEQ ID NO: 42, SEQ ID NO: 43, or afragment thereof, or a sequence having at least 90% identity thereto.

In another illustrative embodiment, the EBD polypeptide sequence isnegatively charged and the amino acid residues are disorder-promotingamino acid residues selected from P, Q, S, G, D and E. In a morespecific embodiment, the disorder-promoting amino acid residues P, Q, S,G, D and E are present in about the following amino acid ratios:D:E:P:Q:S:G=1:2:3:1:2:1. In a more specific embodiment, the EDBpolypeptide comprises the sequence set forth in SEQ ID NO: 44, or afragment thereof, or a sequence having at least 85% identity theretosuch as the sequence set forth in SEQ ID NO: 45.

In yet another illustrative embodiment, the EBD polypeptide sequence isneutral and the disorder-promoting residues are selected from P, Q, Sand G. In a more particular embodiment, the amino acid residues P, Q, Sand G are present in about the amino acid ratio of G:P:Q:S=1:2:1:2. In amore particular embodiment, the EDB polypeptide comprises the sequenceset forth in SEQ ID NO: 11, SEQ ID NO: 27, or SEQ ID NO: 28, or afragment thereof, or a sequence having at least 90% identity thereto.

In another illustrative embodiment, the EBD polypeptide sequence ispositively charged and the amino acid residues are disorder-promotingamino acid residues selected from P, Q, S and R. In a more specificembodiment, the amino acid residues R, P, Q and S are present in aboutthe following amino acid ratios: R:P:Q:S=1:2:1:2, R:P:Q:S=2:2:1:2,R:P:Q:S=3:2:1:2, R:P:Q:S=4:2:1:2, or R:P:Q:S=5:2:1:2.

In another illustrative embodiment, the EBD polypeptide sequence isnegatively charged and the amino acid residues are disorder-promotingamino acid residues are selected from P, Q, S and D. In a moreparticular embodiment, the amino acid residues D, P, Q and S are presentin about the following amino acid ratios: D:P:Q:S=1:2:1:2,D:P:Q:S=2:2:1:2, D:P:Q:S=3:2:1:2, D:P:Q:S=4:2:1:2, or D:P:Q:S=5:2:1:2.

A fusion polypeptide of the invention, comprising an EBD sequence and aheterologous polypeptide sequence, exhibits improved solubility relativeto the corresponding heterologous polypeptide in the absence of the EBDsequence. In a related embodiment, the fusion polypeptide has at least5% increased solubility relative to the heterologous polypeptidesequence, at least 25% increased solubility relative to the heterologouspolypeptide sequence, or at least 50% increased solubility relative tothe heterologous polypeptide sequence.

In another embodiment, a fusion polypeptide of the invention exhibitsreduced aggregation relative to the level of aggregation of theheterologous polypeptide sequence in the absence of the EBD sequence.For example, a fusion polypeptide of the invention generally exhibits atleast 10% reduced aggregation relative to the heterologous polypeptidesequence or at least 25% reduced aggregation relative to theheterologous polypeptide sequence.

In another embodiment, a fusion polypeptide of the invention exhibitsimproved self-folding relative to the heterologous polypeptide sequencein the absence of the EBD sequence.

In another embodiment of the present invention, an EBD sequence employedin a fusion polypeptide comprises an amino acid sequence that maintainsa substantially random coil conformation.

In another embodiment, the EBD sequence of a fusion polypeptide of theinvention comprises an amino acid sequence that is substantiallymutually repulsive.

In another embodiment, the EBD sequence of a fusion polypeptide of theinvention comprises an amino acid sequence that remains in substantiallyconstant motion.

In another embodiment of the present invention, the EBD sequence of afusion polypeptide of the invention is a random sequence ofdisorder-promoting amino acid residues.

The EBD sequence of a fusion polypeptide of the invention generallycomprises between about 5 to 1000 amino acid residues, 5 to 500 aminoacid residues, 5 to 400 amino acid residues, 5 to 300 amino acidresidues, 5 to 200 amino acid residues, 5 to 100 amino acid residues, 5to 80 amino acid residues, 5 to 60 amino acid residues, 5 to 40 aminoacid residues, 5 to 30 amino acid residues, 5 to 20 amino acid residues,10 to 30 amino acid residues, 15 to 25 amino acid residues, 10 to 90amino acid residues, 20 to 80 amino acid residues, 20 to 40 amino acidresidues, 30 to 70 amino acid residues, or 40 to 60 amino acid residues.

In a related embodiment, the disorder-promoting EBD sequence comprisesno more than about 20 amino acid residues, 30 amino acid residues, 40amino acid residues, 50 amino acid residues, 100 amino acid residues,200 amino acid residues, 300 amino acid residues, 400 amino acidresidues, 500 amino acid residues, or 1000 amino acid residues.

In yet another related embodiment, the EBD sequence of a fusionpolypeptide of the invention comprises at least 2-100 repeats of an EBDsequence set forth above or described herein, or a combination thereof.

In another embodiment, the EBD sequence of a fusion polypeptide of theinvention comprises a combination of any one or more of fragmentsderived from disorder-promoting EBD sequences that are positivelycharged, negatively charges, or neutral as set here herein.

In another embodiment, an EBD sequence of a fusion polypeptide of theinvention is cleavable, e.g., can be removed and/or separated from theheterologous polypeptide sequence after recombinant expression by, forexample, enzymatic or chemical cleavage methods.

In another embodiment, an EBD sequence of a fusion polypeptide of theinvention is covalently linked at the N-terminus of the heterologouspolypeptide sequence of interest. In another embodiment, an EBD sequenceof a fusion polypeptide of the invention is covalently linked at theC-terminus of the heterologous polypeptide sequence of interest. In yetanother embodiment, an EBD sequence of a fusion polypeptide of theinvention is covalently linked at the N- and C-termini of theheterologous polypeptide sequence of interest.

In another embodiment of the invention, the charge of an EBD sequence ofa fusion polypeptide of the invention is modulated by, for example,enzymatic and/or chemical methods, in order to modulate the activity ofthe EBD sequence. In a particular embodiment, the charge of the EBDsequence is modulated by phosphorylation.

According to another aspect of the invention, an isolated polynucleotideis provided, wherein the polynucleotide encodes a fusion polypeptide asdescribed herein or an artificial EBD sequence as described herein.

According to yet another aspect of the invention, there is provided anexpression vector comprising an isolated polynucleotide encoding afusion polypeptide as described herein or an artificial EBD sequence asdescribed herein. In a related embodiment, an expression vector isprovided comprising a polynucleotide encoding an EBD sequence andfurther comprising a cloning site for insertion of a polynucleotideencoding a heterologous polypeptide of interest.

According to yet another aspect of the invention, there is provided ahost cell comprising an expression vector as described herein.

According to yet another aspect of the invention, there is provided akit comprising an isolated polynucleotide as described herein, anisolated polypeptide as described herein and/or an isolated host cell asdescribed herein.

Yet another aspect of the invention provides a method for producing arecombinant protein comprising the steps of: introducing into a hostcell an expression vector comprising a polynucleotide sequence encodinga fusion polypeptide, the fusion polypeptide comprising at least one EBDsequence and at least one polypeptide sequence of interest; andexpressing the fusion polypeptide in the host cell. In anotherembodiment, the method further comprises the step of isolating thefusion polypeptide from the host cell. In another related embodiment,the method further comprises the step of removing the EBD sequence fromthe fusion polypeptide before or after isolating the fusion polypeptidefrom the host cell.

These and other aspects of the present invention will become apparentupon reference to the following detailed description. All referencesdisclosed herein and in the enclosed Application Data Sheet are herebyincorporated by reference in their entirety as if each was incorporatedindividually.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1. Amino acid composition, relative to the set of globular proteinsGlobular-3D, of intrinsically disordered regions 10 residues or longerfrom the DisProt database. Slanted hash marks indicate DisProt 1.0 (152proteins), while white indicates DisProt 3.4 (460 proteins). Amino acidcompositions were calculated per disordered regions and then averaged.The arrangement of the amino acids is by peak height for the DisProt 3.4release. Confidence intervals were estimated using per-proteinbootstrapping with 10,000 iterations.

FIGS. 2A and 2B. Amino acid sequence of the randomly generatedartificial EB containing the chosen residues in the followingproportion: X:P:Q:S=1:2:1:2 (SEQ ID NO:35); X=K, E or G (2A) andsequences of positive, negative and neutral bristles, indicated as EB.(SEQ ID NO:24), EB₊ (SEQ ID NO:26) and EB₀ (SEQ ID NO:28)(2B),respectively. The actual X:P:Q:S ratios for these sequences was5:8:6:11, numbers that are close to the 1:2:1:2 used to generate thesequences.

FIG. 3. Ligation of two DNA sequences via PCR. I, amplification of DNA1and DNA2 sequences using reversed DNA1 overlapping primer P2 and DNA2forward overlapping primer P3. II, Products of the PCR1 bearingoverlapping fragments. III, PCR2 annealing step. IV. Final productcomposed of DNA1+DNA2.

FIGS. 4A and 4B. Expression and solubility of ten C. thermocellumproteins with N-terminal entropic bristles induced at 37° C. (4A), orMBP-fusions induced at 37° C. and 30° C. (4B). Abbreviations: T, totalprotein, S, soluble protein, U, uninduced cells. IDs of solubilizedproteins and the corresponding EBDs are shown initalics.

FIG. 5. Vector map of the pAquoProt and pAquoKin E. coli expressionplasmids that have been created to harbor entropic bristles. ThepAquoProt and pAquoKin vectors are identical except within theexpression/cloning region.

FIG. 6. Double stranded sequence of the expression/cloning region of thepAquoProt plasmid (SEQ ID NOS: 54 and 55). The expression/cloning regionis comprised of the T7 promoter/operator, ribosomal binding site (RBS),coding sequences for a 6×His tag and enterokinase (EK) cleavage site,multicloning site, coding sequences for HA epitope tag, and T7terminator (SEQ ID NO:56). The restriction enzymes listed are uniquesites not present elsewhere in the plasmid. Entropic bristle domaincoding sequences are introduced into the expression/cloning region atthe BstBI site positioned between the 6×His tag and EK cleavage codingsequences.

FIG. 7. Double stranded sequence of the expression/cloning region of thepAquoKin plasmid (SEQ ID NOS: 57 and 58). The expression/cloning regionis comprised of the T7 promoter/operator, ribosomal binding site (RBS),coding sequences for a 6×His tag and enterokinase cleavage site,multicloning site, coding sequences for the FLAG™ epitope tag, and T7terminator (SEQ ID NO:59). The restriction enzymes listed are uniquesites not present elsewhere in the plasmid. Entropic bristle domaincoding sequences are introduced into the pAquoKin expression/cloningregion at the BstBI site positioned between the 6×His tag and EKcleavage coding sequences and at the Eco47III site following theC-terminal FLAG™ coding sequence.

FIGS. 8A, 8B, 8C, and 8D. Expression and solubility of TIMP2 with avariety of N-terminal entropic bristles ranging in length from 24 to 250amino acids or 6×His-EK control fusion (8A). Expression and solubilityof TEV protease fused with 3 EBDs that are comprised of the same aminoacids but have distinct primary amino acid sequences (8B). Expressionand solubility of TNSF13b fused with a 120 amino acid EBD or a 60 aminoacid fragment (8C). Expression and solubility of c-Src kinase with anN-terminal fusion or N-and C-terminal EBD fusions. c-Src with entropicbristles fused to both termini is more soluble than N-terminal c-Srcfusions (8D). Abbreviations: T, total protein, S, soluble protein, P,insoluble pellet protein. IDs of solubilized proteins are shown beloweach set of blots.

BRIEF DESCRIPTION OF THE SEQUENCE IDENTIFIERS

SEQ ID NO: 1 is the amino acid sequence of a positively charged EBDdomain, EBD(+), which is a random sequence containing disorder-promotingresidues P, Q, S and K in about the following amino acid ratios:K:P:Q:S=1:2:1:2. The sequence was produced using the random sequencegenerator tool located at the Swiss-Prot website:http://au.expasy.org/tools/randseq.html.

SEQ ID NO: 2 is the amino acid sequence of a positively charged EBDdomain, EBD(++), which is a random sequence containingdisorder-promoting residues P, Q, S and K in about the following aminoacid ratios: K:P:Q:S=2:2:1:2. The sequence was produced using the randomsequence generator tool located at the Swiss-Prot website:http://au.expasy.org/tools/randseq.html.

SEQ ID NO: 3 is the amino acid sequence of a positively charged EBDdomain, EBD(+++), which is a random sequence containingdisorder-promoting residues P, Q, S and K in about the following aminoacid ratios: K:P:Q:S=3:2:1:2. The sequence was produced using the randomsequence generator tool located at the Swiss-Prot website:http://au.expasy.org/tools/randseq.html.

SEQ ID NO: 4 is the amino acid sequence of a positively charged EBDdomain, EBD(++++), which is a random sequence containingdisorder-promoting residues P, Q, S and K in about the following aminoacid ratios: K:P:Q:S=4:2:1:2. The sequence was produced using the randomsequence generator tool located at the Swiss-Prot website:http://au.expasy.org/tools/randseq.html.

SEQ ID NO: 5 is the amino acid sequence of a positively charged EBDdomain, EBD(+++++), which is a random sequence containingdisorder-promoting residues P, Q, S and K in about the following aminoacid ratios: K:P:Q:S=5:2:1:2. The sequence was produced using the randomsequence generator tool located at the Swiss-Prot website:http://au.expasy.org/tools/randseq.html.

SEQ ID NO: 6 is the amino acid sequence of a negatively charged EBDdomain, EBD(−), which is a random sequence containing disorder-promotingresidues P, Q, S and E in about the following amino acid ratios:E:P:Q:S=1:2:1:2. The sequence was produced using the random sequencegenerator tool located at the Swiss-Prot website:http://au.expasy.org/tools/randseq.html.

SEQ ID NO: 7 is the amino acid sequence of a negatively charged EBDdomain, EBD(−−), which is a random sequence containingdisorder-promoting residues P, Q, S and E in about the following aminoacid ratios: E:P:Q:S=2:2:1:2. The sequence was produced using the randomsequence generator tool located at the Swiss-Prot website:http://au.expasy.org/tools/randseq.html.

SEQ ID NO: 8 is the amino acid sequence of a negatively charged EBDdomain, EBD(−−−), which is a random sequence containingdisorder-promoting residues P, Q, S and E in about the following aminoacid ratios: E:P:Q:S=3:2:1:2. The sequence was produced using the randomsequence generator tool located at the Swiss-Prot website:http://au.expasy.org/tools/randseq.html.

SEQ ID NO: 9 is the amino acid sequence of a negatively charged EBDdomain, EBD(−−−−), which is a random sequence containingdisorder-promoting residues P, Q, S and E in about the following aminoacid ratios: E:P:Q:S=4:2:1:2. The sequence was produced using the randomsequence generator tool located at the Swiss-Prot website:http://au.expasy.org/tools/randseq.html.

SEQ ID NO: 10 is the amino acid sequence of a negatively charged EBDdomain, EBD(−−−−−) which is a random sequence containingdisorder-promoting residues P, Q, S and E in about the following aminoacid ratios: E:P:Q:S=5:2:1:2. The sequence was produced using the randomsequence generator tool located at the Swiss-Prot website:http://au.expasy.org/tools/randseq.html.

SEQ ID NO: 11 is the amino acid sequence of a neutral EBD domain,EBD(0), which is a random sequence containing disorder-promotingresidues P, Q, S and G in about the following amino acid ratios:G:P:Q:S=1:2:1:2. The sequence was produced using the random sequencegenerator tool located at the Swiss-Prot website:http://au.expasy.org/tools/randseq.html.

SEQ ID NO: 12 is a polynucleotide sequence encoding the amino acidsequence of SEQ ID NO: 1. Sequence was produced using the reversetranslation tool located at:www.vivo.colostate.edu/molkit/rtranslate/index.html.

SEQ ID NO: 13 is a polynucleotide sequence encoding the amino acidsequence of SEQ ID NO: 2. Sequence was produced using the reversetranslation tool located at:www.vivo.colostate.edu/molkit/rtranslate/index.html.

SEQ ID NO: 14 is a polynucleotide sequence encoding the amino acidsequence of SEQ ID NO: 3. Sequence was produced using the reversetranslation tool located at:www.vivo.colostate.edu/molkit/rtranslate/index.html.

SEQ ID NO: 15 is a polynucleotide sequence encoding the amino acidsequence of SEQ ID NO: 4. Sequence was produced using the reversetranslation tool located at:www.vivo.colostate.edu/molkit/rtranslate/index.html.

SEQ ID NO: 16 is a polynucleotide sequence encoding the amino acidsequence of SEQ ID NO: 5. Sequence was produced using the reversetranslation tool located at:www.vivo.colostate.edu/molkit/rtranslate/index.html.

SEQ ID NO: 17 is a polynucleotide sequence encoding the amino acidsequence of SEQ ID NO: 6. Sequence was produced using the reversetranslation tool located at:www.vivo.colostate.edu/molkit/rtranslate/index.html.

SEQ ID NO: 18 is a polynucleotide sequence encoding the amino acidsequence of SEQ ID NO: 7. Sequence was produced using the reversetranslation tool located at:www.vivo.colostate.edu/molkit/rtranslate/index.html.

SEQ ID NO: 19 is a polynucleotide sequence encoding the amino acidsequence of SEQ ID NO: 8. Sequence was produced using the reversetranslation tool located at:www.vivo.colostate.edu/molkit/rtranslate/index.html.

SEQ ID NO: 20 is a polynucleotide sequence encoding the amino acidsequence of SEQ ID NO: 9. Sequence was produced using the reversetranslation tool located at:www.vivo.colostate.edu/molkit/rtranslate/index.html.

SEQ ID NO: 21 is a polynucleotide sequence encoding the amino acidsequence of SEQ ID NO: 10. Sequence was produced using the reversetranslation tool located at:www.vivo.colostate.edu/molkit/rtranslate/index.html.

SEQ ID NO: 22 is a polynucleotide sequence encoding the amino acidsequence of SEQ ID NO: 11. Sequence was produced using the reversetranslation tool located at:www.vivo.colostate.edu/molkit/rtranslate/index.html.

SEQ ID NO: 23 is the amino acid sequence of a positively charged EBDdomain, EBD(+), which is a random sequence containing disorder-promotingresidues P, Q, S and K in about the following amino acid ratios:K:P:Q:S=1:2:1:2.

The sequence was produced using the random sequence generator toollocated at the Swiss-Prot website:http://au.expasy.org/tools/randseq.html.

SEQ ID NO: 24 is the amino acid sequence of a positively charged EBDdomain of SEQ ID NO: 23.

SEQ ID NO: 25 is the amino acid sequence of a negatively charged EBDdomain, EBD(−), which is a random sequence containing disorder-promotingresidues P, Q, S and E in about the following amino acid ratios:E:P:Q:S=1:2:1:2. The sequence was produced using the random sequencegenerator tool located at the Swiss-Prot website:http://au.expasy.org/tools/randseq.html.

SEQ ID NO: 26 is the amino acid sequence of a negatively charged EBDdomain of SEQ ID NO: 25.

SEQ ID NO: 27 is the amino acid sequence of a neutral EBD domain,EBD(0), which is a random sequence containing disorder-promotingresidues P, Q, S and G in about the following amino acid ratios:G:P:Q:S=1:2:1:2. The sequence was produced using the random sequencegenerator tool located at the Swiss-Prot website:http://au.expasy.org/tools/randseq.html.

SEQ ID NO: 28 is the amino acid sequence of a neutral EBD domain of SEQID NO: 27.

SEQ ID NO: 29 is a polynucleotide sequence encoding the amino acidsequence of SEQ ID NO: 23. The sequence was produced using the reversetranslation tool located at:www.vivo.colostate.edu/molkit/rtranslate/index.html.

SEQ ID NO: 30 is a polynucleotide sequence encoding the amino acidsequence of SEQ ID NO: 24. The sequence was produced using the reversetranslation tool located at:www.vivo.colostate.edu/molkit/rtranslate/index.html.

SEQ ID NO: 31 is a polynucleotide sequence encoding the amino acidsequence of SEQ ID NO: 25. The sequence was produced using the reversetranslation tool located at:www.vivo.colostate.edu/molkit/rtranslate/index.html.

SEQ ID NO: 32 is a polynucleotide sequence encoding the amino acidsequence of SEQ ID NO: 26. The sequence was produced using the reversetranslation tool located at:www.vivo.colostate.edu/molkit/rtranslate/index.html.

SEQ ID NO: 33 is a polynucleotide sequence encoding the amino acidsequence of SEQ ID NO: 27. The sequence was produced using the reversetranslation tool located at:www.vivo.colostate.edu/molkit/rtranslate/index.html.

SEQ ID NO: 34 is a polynucleotide sequence encoding the amino acidsequence of SEQ ID NO: 28. The sequence was produced using the reversetranslation tool located at:www.vivo.colostate.edu/molkit/rtranslate/index.html.

SEQ ID NO: 35 is the polypeptide sequence of an artificial EBD designedto contain amino acids X:P:Q:S in the following ratio 1:2:1:2, where Xis a variable position to generate positive, negative or neutralbristles, and corresponds to one of K, E, or G respectively.

SEQ ID NO: 36 is the polynucleotide sequence of the pAquoProt expressionvector backbone. The pAquoProt vector was built by adding the F1 originof replication, LacI gene, and customized expression/cloning region toan existing pUC19 plasmid.

SEQ ID NO: 37 is the polynucleotide sequence of the pAquoKin expressionvector backbone. The pAquoProt vector was built by adding the F1 originof replication, LacI gene, and customized expression/cloning region toan existing pUC19 plasmid.

SEQ ID NO: 38 is the amino acid sequence of a negatively charged EBDdomain, which is a random sequence containing disorder-promotingresidues P, Q, S and E in about the following amino acid ratios:E:P:Q:S=1:2:1:1. The sequence was produced using the random sequencegenerator tool located at the Swiss-Prot website:http://au.expasy.org/tools/randseq.html.

SEQ ID NO: 39 is the amino acid sequence of a negatively charged EBDdomain, which is a random sequence containing disorder-promotingresidues P, Q, S and E in about the following amino acid ratios:E:P:Q:S=1:4:1:1. The sequence was produced using the random sequencegenerator tool located at the Swiss-Prot website:http://au.expasy.org/tools/randseq.html.

SEQ ID NO: 40 is the amino acid sequence of a negatively charged EBDdomain, which is a random sequence containing disorder-promotingresidues P, Q, S and E in about the following amino acid ratios:E:P:Q:S=2:2:1:1. The sequence was produced using the random sequencegenerator tool located at the Swiss-Prot website:http://au.expasy.org/tools/randseq.html.

SEQ ID NO: 41 is the amino acid sequence of a negatively charged EBDdomain, which is a random sequence containing disorder-promotingresidues P, Q, G and E in about the following amino acid ratios:E:P:Q:G=1:4:1:1. The sequence was produced using the random sequencegenerator tool located at the Swiss-Prot website:http://au.expasy.org/tools/randseq.html.

SEQ ID NO: 42 is the amino acid sequence of a negatively charged EBDdomain, which is a random sequence containing disorder-promotingresidues P, Q, G and E in about the following amino acid ratios:E:P:Q:G=2:2:1:1. The sequence was produced using the random sequencegenerator tool located at the Swiss-Prot website:http://au.expasy.org/tools/randseq.html.

SEQ ID NO: 43 is the amino acid sequence of a negatively charged EBDdomain, which is a random sequence containing disorder-promotingresidues P, Q, G and E in about the following amino acid ratios:E:P:Q:G=3:2:1:1. The sequence was produced using the random sequencegenerator tool located at the Swiss-Prot website:http://au.expasy.org/tools/randseq.html.

SEQ ID NO: 44 is the amino acid sequence of a negatively charged EBDdomain, which is a random sequence containing disorder-promotingresidues P, Q, S, G, D and E in about the following amino acid ratios:D:E:P:Q:S:G=1:2:3:1:2:1. The sequence was produced using the randomsequence generator tool located at the Swiss-Prot website:http://au.expasy.org/tools/randseq.html.

SEQ ID NO: 45 is the amino acid sequence of a negatively charged EBDdomain, in which certain amino acids in SEQ ID NO: 44 were substitutedwith the hydrophobic amino acids I, L, M, F, and V. The hydrophobicamino acid substitutions comprise approximately 12% of the residues.

SEQ ID NO: 46 is a polynucleotide sequence encoding the amino acidsequence of SEQ ID NO: 38. The sequence was produced using the reversetranslation tool located at:www.vivo.colostate.edu/molkit/rtranslate/index.html.

SEQ ID NO: 47 is a polynucleotide sequence encoding the amino acidsequence of SEQ ID NO: 39. The sequence was produced using the reversetranslation tool located at:www.vivo.colostate.edu/molkit/rtranslate/index.html.

SEQ ID NO: 48 is a polynucleotide sequence encoding the amino acidsequence of SEQ ID NO: 40. The sequence was produced using the reversetranslation tool located at:www.vivo.colostate.edu/molkit/rtranslate/index.html.

SEQ ID NO: 49 is a polynucleotide sequence encoding the amino acidsequence of SEQ ID NO: 41. The sequence was produced using the reversetranslation tool located at:www.vivo.colostate.edu/molkit/rtranslate/index.html.

SEQ ID NO: 50 is a polynucleotide sequence encoding the amino acidsequence of SEQ ID NO: 42. The sequence was produced using the reversetranslation tool located at:www.vivo.colostate.edu/molkit/rtranslate/index.html.

SEQ ID NO: 51 is a polynucleotide sequence encoding the amino acidsequence of SEQ ID NO: 43. The sequence was produced using the reversetranslation tool located at:www.vivo.colostate.edu/molkit/rtranslate/index.html.

SEQ ID NO: 52 is a polynucleotide sequence encoding the amino acidsequence of SEQ ID NO: 44. The sequence was produced using the reversetranslation tool located at:www.vivo.colostate.edu/molkit/rtranslate/index.html.

SEQ ID NO: 53 is a polynucleotide sequence encoding the amino acidsequence of SEQ ID NO: 45. The sequence was produced using the reversetranslation tool located at:www.vivo.colostate.edu/molkit/rtranslate/index.html.

DETAILED DESCRIPTION OF THE INVENTION

Artificial EBD fusion polynucleotides, polypeptides and vectors areprovided by the present invention which offers significant advantages inthe context of recombinant polypeptide production, particularly where itis desired to achieve, for example, improved solubility, improved yield,improved folding and/or reduced aggregation of a recombinant polypeptideof interest.

Artificial EBDs take advantage of the unique features of differentclasses of amino acids that are found within regions of order anddisorder. The amino acids compositions of disordered and ordered regionsin proteins are significantly different. Based on the analysis ofintrinsically disordered proteins and regions within proteins, aminoacids can be grouped into 3 categories: 1) order-promoting, 2)disorder-promoting, and 3) neutral (Dunker et al., Intrinsicallydisordered protein. J Mol Graph Model, 2001. 19(1): p. 26-59).

The advantages of the present invention are made possible by properselection of disorder-promoting residues, order-promoting residuesand/or neutral residues, as well as their respective proportions, withinan artificial EBD sequence, as described herein. Proteins which haveproven difficult to produce by conventional recombinant methodologiescan be successfully produced when employing the artificial EBD sequencesof the present invention.

The term “disorder-promoting amino acid residue” means an amino acidresidue that promotes the disorder of stable tertiary and/or secondarystructure within a polypeptide in solution. Disorder-promoting residuesinclude D, M, K, R, S, Q, P, E and G.

The term “order-promoting amino acid residue” means an amino acidresidue that promotes stable tertiary and/or secondary structure withina polypeptide in solution. Order-promoting amino acid residues includeC, W, Y, I, F, V, L, H, T and N.

Neutral amino acid residues include A. The class of neutral amino acidscan also include H, T, N, G, and D, as these amino acids tend toinfluence the tertiary and/or secondary structures within a protein orpolypeptide to a relatively lesser extent then the other amino acidsresidues in above-defined classes (FIG. 1).

The phrases “about the ratio” and “in about the following amino acidratio” means a group of amino acids as described herein, wherein therange “about” is determined by the actual ratio of said group of aminoacids, first normalized by the lowest integer value within said groupand then rounded to the nearest integer value. The resulting ratio ifidentical to the claimed ratio is then said to be “about” the claimedratio of the group of amino acids. For example, consider a 100 AA EBDsequence of a fusion polypeptide which has the actual amino acid ratioof X:P:Q:S of 30:26:14:32. The actual amino acid ratio is normalized to14, the lowest integer value, to yield a ratio of 2.1:1.9:1:2.3, whichrounded to the nearest integer value is the ratio 2:2:1:2. Thus, a 100AA EBD domain with an actual ratio of 30:26:14:32 has about thefollowing amino acid ratio X:P:Q:S=2:2:1:2.

As used herein, the terms “polypeptide” and “protein” are usedinterchangeably, unless specified to the contrary, and according toconventional meaning, i.e., as a sequence of amino acids. Polypeptidesare not limited to a specific length, e.g., they may comprise a fulllength protein sequence or a fragment of a full length protein, and mayinclude post-translational modifications of the polypeptide, forexample, glycosylations, acetylations, phosphorylations and the like, aswell as other modifications known in the art, both naturally occurringand non-naturally occurring. Polypeptides of the invention may beprepared using any of a variety of well known recombinant and/orsynthetic techniques, illustrative examples of which are furtherdiscussed below.

The practice of the present invention will employ, unless indicatedspecifically to the contrary, conventional methods of molecular biologyand recombinant DNA techniques within the skill of the art, many ofwhich are described below for the purpose of illustration. Suchtechniques are explained fully in the literature. See, e.g., Sambrook,et al., Molecular Cloning: A Laboratory Manual (2nd Edition, 1989);Maniatis et al., Molecular Cloning: A Laboratory Manual (1982); DNACloning: A Practical Approach, vol. I & II (D. Glover, ed.);Oligonucleotide Synthesis (N. Gait, ed., 1984); Nucleic AcidHybridization (B. Hames & S. Higgins, eds., 1985); Transcription andTranslation (B. Hames & S. Higgins, eds., 1984); Animal Cell Culture (R.Freshney, ed., 1986); A Practical Guide to Molecular Cloning (B. Perbal,ed., 1984).

All publications, patents and patent applications cited herein, whethersupra or infra, are hereby incorporated by reference in their entirety.

As used in this specification and the appended claims, the singularforms “a,” “an” and “the” include plural references unless the contentclearly dictates otherwise.

Fusion polypeptides comprising an EBD sequence and a heterologouspolypeptide exhibit improved solubility relative to the correspondingheterologous polypeptide in the absence of the EBD sequence. In oneembodiment, for example, the fusion polypeptide has at least 5%increased solubility relative to the heterologous polypeptide sequencealone. In another related embodiment, the fusion polypeptide has atleast 25% increased solubility relative to the heterologous polypeptidesequence. In yet another related embodiment, the fusion polypeptide hasat least 50% increased solubility relative to the heterologouspolypeptide sequence.

The extent of improved solubility provided by an EBD sequence describedherein can be determined using any of a number of available approaches(see for example, Kapust, R. B. and D.S. Waugh, Escherichia colimaltose-binding protein is uncommonly effective at promoting thesolubility of polypeptides to which it is fused. Protein Sci, 1999.8:1668-74; Fox, J. D., et al., Maltodextrin-binding proteins fromdiverse bacteria and archaea are potent solubility enhancers. FEBS Lett,2003. 537:53-7; Dyson M R, Shadbolt S P, Vincent K J, Perera R L,McCafferty J. Production of soluble mammalian proteins in Escherichiacoli: identification of protein features that correlate with successfulexpression. BMC Biotechnol. 2004 Dec. 14; 4(1):32).

Cells from single, drug resistant colony of E. coli overproducing thefusion polypeptide are grown to saturation in LB broth (Miller J H.1972. Experiments in molecular genetics. Cold Spring Harbor, N.Y.: ColdSpring Harbor Press. p 433) supplemented with 100 mg/mL ampicillin and30 mg/mL chloramphenicol at 37° C. The saturated cultures are diluted50-fold in the same medium and grown in shake-flasks to mid-log phase(A₆₀₀˜0.5-0.7), at which time IPTG is added to a final concentration of1 mM. After 3 h, the cells are recovered by centrifugation. The cellpellets are resuspended in 0.1 culture volumes of lysis buffer (50 mMTris-HCl (pH 8.0), 150 mM NaCl, 1 mM EDTA), and disrupted by sonication.A total protein sample is collected from the cell suspension aftersonication, and a soluble protein sample is collected from thesupernatant after the insoluble debris is pelleted by centrifugation(20,000×g). These samples are subjected to SDS-PAGE and proteins arevisualized by staining with Coomassie Brilliant Blue. At least threeindependent experiments are typically performed to obtain numericalestimates of the solubility of each fusion protein in E. coli.Coomassie-stained gels will be scanned with a gel-scanning densitometerand the pixel densities of the bands corresponding to the fusionproteins are obtained directly by volumetric integration. In each lane,the collective density of all E. coli proteins that are larger than thelargest fusion protein are also determined by volumetric integration andused to normalize the values in each lane relative to the others. Thepercent solubility of each fusion protein is calculated by dividing theamount of soluble fusion protein by the total amount of fusion proteinin the cells, after first subtracting the normalized background valuesobtained from negative control lanes (cells containing no expressionvector). Descriptive statistical data (e.g., the mean and standarddeviation) is then generated using standard methods.

The presence of an EBD sequence in fusion polypeptides of the presentinvention can also serve to reduce the extent of aggregation of aheterologous polypeptide sequence. In one embodiment, for example, thefusion polypeptide exhibits at least 10% reduced aggregation relative tothe heterologous polypeptide. In another embodiment, the fusionpolypeptide has at least 25% reduced aggregation relative to theheterologous polypeptide.

The extent of reduced aggregation provided by the fusion polypeptides ofthe present invention can be determined using any of a number ofavailable techniques (see for example, Kapust, R. B. and D.S. Waugh,Escherichia coli maltose-binding protein is uncommonly effective atpromoting the solubility of polypeptides to which it is fused. ProteinSci, 1999. 8:1668-74; Fox, J. D., et al., Maltodextrin-binding proteinsfrom diverse bacteria and archaea are potent solubility enhancers. FEBSLett, 2003. 537:53-7).

Cells from single, drug resistant colony of E. coli overproducing thefusion polypeptide are grown to saturation in LB broth (Miller J H.1972. Experiments in molecular genetics. Cold Spring Harbor, N.Y.: ColdSpring Harbor Press. p 433) supplemented with 100 mg/mL ampicillin and30 mg/mL chloramphenicol at 37° C. The saturated cultures are diluted50-fold in the same medium and grown in shake-flasks to mid-log phase(A₆₀₀˜0.5-0.7), at which time IPTG is added to a final concentration of1 mM. After 3 h, the cells are recovered by centrifugation. The cellpellets are resuspended in 0.1 culture volumes of lysis buffer (50 mMTris-HCl (pH 8.0), 150 mM NaCl, 1 mM EDTA), and disrupted by sonication.A total protein sample is collected from the cell suspension aftersonication, and an insoluble protein sample is collected from the pelletafter the centrifugation (20,000×g). These samples are subjected toSDS-PAGE and proteins are visualized by staining with CoomassieBrilliant Blue. At least three independent experiments are typicallyperformed to obtain numerical estimates of the solubility of each fusionprotein in E. coli. Coomassie-stained gels are scanned with agel-scanning densitometer and the pixel densities of the bandscorresponding to the fusion proteins are obtained directly by volumetricintegration. In each lane, the collective density of all insoluble E.coli proteins that are larger than the largest fusion protein is alsodetermined by volumetric integration and used to normalize the values ineach lane relative to the others. The percent insolubility of eachfusion protein is calculated by dividing the amount of insoluble fusionprotein by the total amount of fusion protein in the cells, after firstsubtracting the normalized background values obtained from negativecontrol lanes (cells containing no expression vector). Descriptivestatistical data (e.g., the mean and standard deviation) is generated bystandard methods.

The presence of an EBD sequence in the fusion polypeptides of thepresent invention can also serve to improve the folding characteristicsof the fusion polypeptides relative to the corresponding heterologouspolypeptide, e.g., by minimizing interference caused by interaction withother proteins.

Assays for evaluating the folding characteristics of a fusionpolypeptide of the invention can be carried out using conventionaltechniques, such as circular dichroism spectroscopy in far ultra-violetregion, circular dichroism in near ultra-violet region, nuclear magneticresonance spectroscopy, infra-red spectroscopy, Raman spectroscopy,intrinsic fluorescence spectroscopy, extrinsic fluorescencespectroscopy, fluorescence resonance energy transfer, fluorescenceanisotropy and polarization, steady-state fluorescence, time-domainfluorescence, numerous hydrodynamic techniques including gel-filtration,viscometry, small-angle X-ray scattering, small angle neutronscattering, dynamic light scattering, static light scattering, scanningmicrocalorimetry, and limited proteolysis.

In another embodiment of the invention, an EBD comprises an amino acidsequence that maintains a substantially random coil conformation.Whether a given amino acid sequence maintains a substantially randomcoil conformation can be determined by circular dichroism spectroscopyin far ultra-violet region, nuclear magnetic resonance spectroscopy,infra-red spectroscopy, Raman spectroscopy, fluorescence spectroscopy,numerous hydrodynamic techniques including gel-filtration, viscometry,small-angle X-ray scattering, small angle neutron scattering, dynamiclight scattering, static light scattering, scanning microcalorimetry,and limited proteolysis.

In another embodiment of the invention, an EBD sequence comprises anamino acid sequence that is substantially mutually repulsive. Thisproperty of being mutually repulsive can be determined by simplecalculations of charge distribution within the polypeptide sequence.

In yet another embodiment of the invention, an EBD sequence comprises anamino acid sequence that remains in substantially constant motion,particularly in an aqueous environment. The property of being insubstantially constant motion can be determined by nuclear magneticresonance spectroscopy, small-angle X-ray scattering, small angleneutron scattering, dynamic light scattering, intrinsic fluorescencespectroscopy, extrinsic fluorescence spectroscopy, fluorescenceresonance energy transfer, fluorescence anisotropy and polarization,steady-state fluorescence, time-domain fluorescence.

In another embodiment, the fusion polypeptides of the invention furthercomprise independent cleavable linkers, which allow an EBD sequence, forexample at either the N or C terminus, to be easily cleaved from aheterologous polypeptide sequence of interest. Such cleavable linkersare known and available in the art. This embodiment thus providesimproved isolation and purification of a heterologous polypeptidesequence and facilitates downstream high-throughput processes.

The present invention also provides polypeptide fragments of an EBDpolypeptide sequence described herein, wherein the fragment comprises atleast about 5, 10, 15, 20, 25, 50, or 100 contiguous amino acids, ormore, including all intermediate lengths, of an EBD polypeptide sequenceset forth herein, or those encoded by a polynucleotide sequence setforth herein. In a preferred embodiment, an EBD fragment providessimilar or improved activity relative to the activity of the EBDsequence from which it is derived (wherein the activity includes, forexample, one or more of improved solubility, improved folding, reducedaggregation and/or improved yield, when in fusion with a heterologouspolypeptide sequence of interest.

In another aspect, the present invention provides variants of an EBDpolypeptide sequence described herein. EBD polypeptide variants willtypically exhibit at least about 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%,94%, 95%, 96%, 97%, 98%, or 99% or more identity (e.g., determined asdescribed below), along its length, to an EBD polypeptide sequence setforth herein. Preferably the EBD variant provides similar or improvedactivity relative to the activity of the EBD sequence from which thevariant was derived (wherein the activity includes one or more ofimproved solubility, improved folding, reduced aggregation and/orimproved yield, when in fusion with a heterologous polypeptide sequenceof interest.

An EBD polypeptide variant thus refers to a polypeptide that differsfrom an EBD polypeptide sequence disclosed herein in one or moresubstitutions, deletions, additions and/or insertions. Such variants maybe naturally occurring or may be synthetically generated, for example,by modifying one or more of the EBD polypeptide sequences of theinvention and evaluating their activity as described herein and/or usingany of a number of techniques well known in the art.

In certain instances, a variant will contain conservative substitutions.A “conservative substitution” is one in which an amino acid issubstituted for another amino acid that has similar properties, suchthat one skilled in the art of peptide chemistry would expect thesecondary structure and hydropathic nature of the polypeptide to besubstantially unchanged. As described above, modifications may be madein the structure of the EBD polynucleotides and polypeptides of thepresent invention and still obtain a functional molecule that encodes avariant or derivative polypeptide with desirable activity. When it isdesired to alter the amino acid sequence of an EBD polypeptide to createan equivalent or an improved EBD variant or EBD fragment, one skilled inthe art can readily change one or more of the codons of the encoding DNAsequence, for example according to Table 1.

For example, certain amino acids may be substituted for other aminoacids in a protein structure without appreciable loss of desiredactivity. It is thus contemplated that various changes may be made inthe EBD polypeptide sequences of the invention, or corresponding DNAsequences which encode said EBD polypeptide sequences, withoutappreciable loss of their desired activity.

TABLE 1 Amino Acids Codons Alanine Ala A GCA GCC GCG GCU Cysteine Cys CUGC UGU Aspartic acid Asp D GAC GAU Glutamic acid Glu E GAA GAGPhenylalanine Phe F UUC UUU Glycine Gly G GGA GGC GGG GGU Histidine HisH CAC CAU Isoleucine Ile I AUA AUC AUU Lysine Lys K AAA AAG Leucine LeuL UUA UUG CUA CUC CUG CUU Methionine Met M AUG Asparagine Asn N AAC AAUProline Pro P CCA CCC CCG CCU Glutamine Gln Q CAA CAG Arginine Arg R AGAAGG CGA CGC CGG CGU Serine Ser S AGC AGU UCA UCC UCG UCU Threonine Thr TACA ACC ACG ACU Valine Val V GUA GUC GUG GUU Tryptophan Trp W UGGTyrosine Tyr Y UAC UAU

In making such changes, the hydropathic index of amino acids may also beconsidered. The importance of the hydropathic amino acid index inconferring interactive biologic function on a protein is generallyunderstood in the art (Kyte and Doolittle, 1982, incorporated herein byreference). It is accepted that the relative hydropathic character ofthe amino acid contributes to the secondary structure of the resultantprotein, which in turn has potential bearing on the interaction of theprotein with other molecules, for example, enzymes, substrates,receptors, DNA, antibodies, antigens, and the like. Each amino acid hasbeen assigned a hydropathic index on the basis of its hydrophobicity andcharge characteristics (Kyte and Doolittle, 1982). These values are:isoleucine (+4.5); valine (+4.2); leucine (+3.8); phenylalanine (+2.8);cysteine/cystine (+2.5); methionine (+1.9); alanine (+1.8); glycine(−0.4); threonine (−0.7); serine (−0.8); tryptophan (−0.9); tyrosine(−1.3); proline (−1.6); histidine (−3.2); glutamate (−3.5); glutamine(−3.5); aspartate (−3.5); asparagine (−3.5); lysine (−3.9); and arginine(−4.5).

Therefore, according to certain embodiments, amino acids within an EBDsequence of the invention may be substituted by other amino acids havinga similar hydropathic index or score. Preferably, any such changesresult in an EBD sequence with a similar level of activity as theunmodified EBD sequence. In making such changes, the substitution ofamino acids whose hydropathic indices are within ±2 is preferred, thosewithin ±1 are particularly preferred, and those within ±0.5 are evenmore particularly preferred. It is also understood in the art that thesubstitution of like amino acids can be made effectively on the basis ofhydrophilicity. As detailed in U.S. Pat. No. 4,554,101, the followinghydrophilicity values have been assigned to amino acid residues:arginine (+3.0); lysine (+3.0); aspartate (+3.0±1); glutamate (+3.0±1);serine (+0.3); asparagine (+0.2); glutamine (+0.2); glycine (0);threonine (−0.4); proline (−0.5±1); alanine (−0.5); histidine (−0.5);cysteine (−1.0); methionine (−1.3); valine (−1.5); leucine (−1.8);isoleucine (−1.8); tyrosine (−2.3); phenylalanine (−2.5); tryptophan(−3.4). Thus, an amino acid can be substituted for another having asimilar hydrophilicity value and in many cases still retain a desiredlevel of activity. In such changes, the substitution of amino acidswhose hydrophilicity values are within ±2 is preferred, those within ±1are particularly preferred, and those within ±0.5 are even moreparticularly preferred.

As outlined above, amino acid substitutions are generally thereforebased on the relative similarity of the amino acid side-chainsubstituents, for example, their hydrophobicity, hydrophilicity, charge,size, and the like.

Amino acid substitutions within an EBD sequence of the invention mayfurther be made on the basis of similarity in polarity, charge,solubility, hydrophobicity, hydrophilicity and/or the amphipathic natureof the residues. For example, negatively charged amino acids includeaspartic acid and glutamic acid; positively charged amino acids includelysine and arginine; and amino acids with uncharged polar head groupshaving similar hydrophilicity values include leucine, isoleucine andvaline; glycine and alanine; asparagine and glutamine; and serine,threonine, phenylalanine and tyrosine. Other groups of amino acids thatmay represent conservative changes include: (1) ala, pro, gly, glu, asp,gln, asn, ser, thr; (2) cys, ser, tyr, thr; (3) val, ile, leu, met, ala,phe; (4) lys, arg, his; and (5) phe, tyr, trp, his. A variant may also,or alternatively, contain nonconservative changes.

In an illustrative embodiment, a variant EBD polypeptide differs fromthe corresponding unmodified EBD sequence by substitution, deletion oraddition of five percent of the original amino acids or fewer. Variantsmay also (or alternatively) be modified by, for example, the deletion oraddition of amino acids that have minimal influence on the desiredactivity.

A polypeptide of the invention may further comprise a signal (or leader)sequence at the N-terminal end of the polypeptide, whichco-translationally or post-translationally directs transfer of theprotein. The polypeptide may also be conjugated to a linker or othersequence for ease of synthesis, purification or identification of thepolypeptide (e.g., poly-His), or to enhance binding of the polypeptideto a solid support.

As noted above, the present invention provides EBD polypeptide variantsequences which share some degree of sequence identity with an EBDpolypeptide specifically described herein, such as those having at least40%, 50%, 60%, 70%, 80%, 90% or 95% identity with an EBD polypeptidesequence described herein. When comparing polypeptide sequences toevaluate their extent of shared sequence identity, two sequences aresaid to be “identical” if the sequence of amino acids in the twosequences is the same when aligned for maximum correspondence, asdescribed below. Comparisons between two sequences are typicallyperformed by comparing the sequences over a comparison window toidentify and compare local regions of sequence similarity. A “comparisonwindow” as used herein, refers to a segment of at least about 20contiguous positions, usually 30 to about 75, 40 to about 50, in which asequence may be compared to a reference sequence of the same number ofcontiguous positions after the two sequences are optimally aligned.

Optimal alignment of sequences for comparison may be conducted using theMegalign program in the Lasergene suite of bioinformatics software(DNASTAR, Inc., Madison, Wis.), using default parameters. This programembodies several alignment schemes described in the followingreferences: Dayhoff, M. O., (1978) A model of evolutionary change inproteins—Matrices for detecting distant relationships. In Dayhoff, M. O.(ed.) Atlas of Protein Sequence and Structure, National BiomedicalResearch Foundation, Washington D.C. Vol. 5, Suppl. 3, pp. 345-358; HeinJ. (1990) Unified Approach to Alignment and Phylogenes, pp. 626-645Methods in Enzymology vol. 183, Academic Press, Inc., San Diego, Calif.;Higgins, D. G. and Sharp, P. M., CABIOS 5:151-153 (1989); Myers, E. W.and Muller W., CABIOS 4:11-17 (1988); Robinson, E. D., Comb. Theor11:105 (1971); Saitou, N. Nei, M., Mol. Biol. Evol. 4:406-425 (1987);Sneath, P. H. A. and Sokal, R. R., Numerical Taxonomy—the Principles andPractice of Numerical Taxonomy, Freeman Press, San Francisco, Calif.(1973); Wilbur, W. J. and Lipman, D. J., Proc. Natl. Acad., Sci. USA80:726-730 (1983).

Alternatively, optimal alignment of sequences for comparison may beconducted by the local identity algorithm of Smith and Waterman, Add.APL. Math 2:482 (1981), by the identity alignment algorithm of Needlemanand Wunsch, J. Mol. Biol. 48:443 (1970), by the search for similaritymethods of Pearson and Lipman, Proc. Natl. Acad. Sci. USA 85: 2444(1988), by computerized implementations of these algorithms (GAP,BESTFIT, BLAST, FASTA, and TFASTA in the Wisconsin Genetics SoftwarePackage, Genetics Computer Group (GCG), 575 Science Dr., Madison, Wis.),or by inspection.

One preferred example of algorithms that are suitable for determiningpercent sequence identity and sequence similarity are the BLAST andBLAST 2.0 algorithms, which are described in Altschul et al., Nucl.Acids Res. 25:3389-3402 (1977), and Altschul et al., J. Mol. Biol.215:403-410 (1990), respectively. BLAST and BLAST 2.0 can be used, forexample with the parameters described herein, to determine percentsequence identity for the polynucleotides and polypeptides of theinvention. Software for performing BLAST analyses is publicly availablethrough the National Center for Biotechnology Information. For aminoacid sequences, a scoring matrix can be used to calculate the cumulativescore. Extension of the word hits in each direction are halted when: thecumulative alignment score falls off by the quantity X from its maximumachieved value; the cumulative score goes to zero or below, due to theaccumulation of one or more negative-scoring residue alignments; or theend of either sequence is reached. The BLAST algorithm parameters W, Tand X determine the sensitivity and speed of the alignment.

In one preferred approach, the “percentage of sequence identity” isdetermined by comparing two optimally aligned sequences over a window ofcomparison of at least 20 positions, wherein the portion of thepolypeptide sequence in the comparison window may comprise additions ordeletions (i.e., gaps) of 20 percent or less, usually 5 to 15 percent,or 10 to 12 percent, as compared to the reference sequences (which doesnot comprise additions or deletions) for optimal alignment of the twosequences. The percentage is calculated by determining the number ofpositions at which the identical amino acid residue occurs in bothsequences to yield the number of matched positions, dividing the numberof matched positions by the total number of positions in the referencesequence (i.e., the window size) and multiplying the results by 100 toyield the percentage of sequence identity.

In another aspect of the invention, there is provided an isolatedpolynucleotide sequence encoding a fusion polypeptide, the fusionpolypeptide comprising at least one EBD sequence and at least oneheterologous polypeptide sequence of interest. In a related aspect, theinvention provides expression vectors comprising a polynucleotideencoding an EBD fusion polypeptide of the invention. In another relatedaspect, an expression vector of the invention comprises a polynucleotideencoding one or more EBD sequence and further comprises a multiplecloning site for the insertion of a polynucleotide encoding aheterologous polypeptide sequence of interest.

Polynucleotides compositions of the present invention may be identified,prepared and/or manipulated using any of a variety of well establishedtechniques (see generally, Sambrook et al., Molecular Cloning: ALaboratory Manual, Cold Spring Harbor Laboratories, Cold Spring Harbor,N.Y., 1989, and other like references).

In addition, any polynucleotide of the invention, such as apolynucleotide encoding an EBD polypeptide sequence, or a vectorcomprising a polynucleotide encoding an EBD polypeptide sequence, may befurther modified to increase stability in vivo. Possible modificationsinclude, but are not limited to, the addition of flanking sequences atthe 5′ and/or 3′ ends; the use of phosphorothioate or 2′ O-methyl ratherthan phosphodiesterase linkages in the backbone; and/or the inclusion ofnontraditional bases such as inosine, queosine and wybutosine, as wellas acetyl- methyl-, thio- and other modified forms of adenine, cytidine,guanine, thymine and uridine.

The terms “DNA” and “polynucleotide” are used essentiallyinterchangeably herein to refer to a DNA molecule that has been isolatedfree of total genomic DNA of a particular species. “Isolated”, as usedherein, means that a polynucleotide is substantially away from othercoding sequences, and that the DNA molecule does not contain largeportions of unrelated coding DNA, such as large chromosomal fragments orother functional genes or polypeptide coding regions. Of course, thisrefers to the DNA molecule as originally isolated, and does not excludegenes or coding regions later added to the segment by the hand of man.

As will be understood by those skilled in the art, the polynucleotidecompositions of this invention can include genomic sequences,extra-genomic and plasmid-encoded sequences and smaller engineered genesegments that express, or may be adapted to express, proteins,polypeptides, peptides and the like. Such segments may be naturallyisolated, or modified synthetically by the hand of man.

As will also be recognized, polynucleotides of the invention may besingle-stranded (coding or antisense) or double-stranded, and may be DNA(genomic, cDNA or synthetic) or RNA molecules. RNA molecules may includeHnRNA molecules, which contain introns and correspond to a DNA moleculein a one-to-one manner, and mRNA molecules, which do not containintrons. Additional coding or non-coding sequences may, but need not, bepresent within a polynucleotide of the present invention, and apolynucleotide may, but need not, be linked to other molecules and/orsupport materials.

In addition to the EBD polynucleotide sequences set forth herein, thepresent invention also provides EBD polynucleotide variants havingsubstantial identity to an EBD polynucleotide sequence disclosed herein,for example those comprising at least 50% sequence identity, preferablyat least, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, or99% or higher, sequence identity compared to an EBD polynucleotidesequence of this invention using the methods described herein, (e.g.,BLAST analysis using standard parameters, as described below). Oneskilled in this art will recognize that these values can beappropriately adjusted to determine corresponding identity ofpolypeptides encoded by two polynucleotide sequences by taking intoaccount codon degeneracy, amino acid similarity, reading framepositioning and the like.

Typically, EBD polynucleotide variants will contain one or moresubstitutions, additions, deletions and/or insertions, preferably suchthat the activity (e.g., improved folding, reduced aggregation and/orimproved yield, when in fusion with a heterologous sequence of interest)of the polypeptide encoded by the variant polynucleotide is notsubstantially diminished relative to the corresponding unmodifiedpolynucleotide sequence.

In additional embodiments, the present invention provides polynucleotidefragments comprising or consisting of various lengths of contiguousstretches of sequence identical to or complementary to one or more ofthe EBD polynucleotide sequences disclosed herein. For example,polynucleotides are provided by this invention that comprise or consistof at least about 15, 20, 30, 40, 50, 75, 100, 150, 200, 300, 400, 500or 1000 or more contiguous nucleotides of one or more of the sequencesdisclosed herein as well as all intermediate lengths there between. Itwill be readily understood that “intermediate lengths”, in this context,means any length between the quoted values, such as 16, 17, 18, 19,etc.; 21, 22, 23, etc.; 30, 31, 32, etc.; 50, 51, 52, 53, etc.; 100,101, 102, 103, etc.; 150, 151, 152, 153, etc.; including all integersthrough 200-500; 500-1,000, and the like. A polynucleotide sequence asdescribed here may be extended at one or both ends by additionalnucleotides not found in the native sequence. This additional sequencemay consist of 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16,17, 18, 19, or 20 nucleotides at either end of the disclosed sequence orat both ends of the disclosed sequence. Preferably, an EBDpolynucleotide fragment of the invention encodes a fusion polypeptidethat retains one or more desired activities, e.g., improved folding,reduced aggregation and/or improved yield, when in fusion with aheterologous sequence of interest.

The EBD polynucleotides of the present invention, or fragments thereof,regardless of the length of the coding sequence itself, may be combinedwith other DNA sequences, such as promoters, polyadenylation signals,additional restriction enzyme sites, multiple cloning sites, othercoding segments, and the like, such that their overall length may varyconsiderably. It is therefore contemplated that a nucleic acid fragmentof almost any length may be employed, with the total length preferablybeing limited by the ease of preparation and use in the intendedrecombinant DNA protocol. For example, illustrative polynucleotidesegments with total lengths of about 10,000, about 5000, about 3000,about 2,000, about 1,000, about 500, about 200, about 100, about 50 basepairs in length, and the like, (including all intermediate lengths) arecontemplated to be useful in many implementations of this invention.

It will be appreciated by those of ordinary skill in the art that, as aresult of the degeneracy of the genetic code, there are many nucleotidesequences that will encode a polypeptide as described herein. Some ofthese polynucleotides bear minimal homology to the native polynucleotidesequence. Nonetheless, polynucleotides that vary due to differences incodon usage are specifically contemplated by the present invention.Further, different alleles of an EBD polynucleotide sequence providedherein are within the scope of the present invention. Alleles areendogenous sequences that are altered as a result of one or moremutations, such as deletions, additions and/or substitutions ofnucleotides. The resulting mRNA and protein may, but need not, have analtered structure or function. Alleles may be identified using standardtechniques (such as hybridization, amplification and/or databasesequence comparison).

In another embodiment of the invention, a mutagenesis approach, such assite-specific mutagenesis, may be employed for the preparation ofvariants and/or derivatives of the EBD polynucleotides and polypeptidesdescribed herein. By this approach, for example, specific modificationsin a polypeptide sequence can be made through mutagenesis of theunderlying polynucleotides that encode them. These techniques provides astraightforward approach to prepare and test sequence variants, forexample, incorporating one or more of the foregoing considerations, byintroducing one or more nucleotide sequence changes into thepolynucleotide.

Site-specific mutagenesis allows the production of mutants through theuse of specific oligonucleotide sequences which encode the DNA sequenceof the desired mutation, as well as a sufficient number of adjacentnucleotides, to provide a primer sequence of sufficient size andsequence complexity to form a stable duplex on both sides of thedeletion junction being traversed. Mutations may be employed in aselected polynucleotide sequence to improve, alter, decrease, modify, orotherwise change the properties of the polynucleotide itself, and/oralter the properties, activity, composition, stability, or primarysequence of the encoded polypeptide.

In certain embodiments, the present invention contemplates themutagenesis of the disclosed polynucleotide sequences to alter one ormore activities/properties of the encoded polypeptide. The techniques ofsite-specific mutagenesis are well-known in the art, and are widely usedto create variants of both polypeptides and polynucleotides. Forexample, site-specific mutagenesis is often used to alter a specificportion of a DNA molecule. In such embodiments, a primer comprisingtypically about 14 to about 25 nucleotides or so in length may beemployed, in about 5 to about 10 residues on both sides of the junctionof the sequence being altered.

As will be appreciated by those of skill in the art, site-specificmutagenesis techniques have often employed a phage vector that exists inboth a single stranded and double stranded form. Typical vectors usefulin site-directed mutagenesis include vectors such as the M13 phage.These phage are readily commercially-available and their use isgenerally well-known to those skilled in the art. Double-strandedplasmids are also routinely employed in site directed mutagenesis thateliminates the step of transferring the gene of interest from a plasmidto a phage.

In general, site-directed mutagenesis in accordance herewith isperformed by first obtaining a single-stranded vector or melting apartof two strands of a double-stranded vector that includes within itssequence a DNA sequence that encodes the desired peptide. Anoligonucleotide primer bearing the desired mutated sequence is prepared,generally synthetically. This primer is then annealed with thesingle-stranded vector, and subjected to DNA polymerizing enzymes suchas E. coli polymerase I Klenow fragment, in order to complete thesynthesis of the mutation-bearing strand. Thus, a heteroduplex is formedwherein one strand encodes the original non-mutated sequence and thesecond strand bears the desired mutation. This heteroduplex vector isthen used to transform appropriate cells, such as E. coli cells, andclones are selected which include recombinant vectors bearing themutated sequence arrangement.

The preparation of sequence variants of the selected peptide-encodingDNA segments using site-directed mutagenesis provides a means ofproducing potentially useful species and is not meant to be limiting asthere are other ways in which sequence variants of peptides and the DNAsequences encoding them may be obtained. For example, recombinantvectors encoding the desired peptide sequence may be treated withmutagenic agents, such as hydroxylamine, to obtain sequence variants.Specific details regarding these methods and protocols are found in theteachings of Maloy et al., 1994; Segal, 1976; Prokop and Bajpai, 1991;Kuby, 1994; and Maniatis et al., 1982, each incorporated herein byreference, for that purpose.

As used herein, the term “oligonucleotide directed mutagenesisprocedure” refers to template-dependent processes and vector-mediatedpropagation which result in an increase in the concentration of aspecific nucleic acid molecule relative to its initial concentration, orin an increase in the concentration of a detectable signal, such asamplification. As used herein, the term “oligonucleotide directedmutagenesis procedure” is intended to refer to a process that involvesthe template-dependent extension of a primer molecule. The term templatedependent process refers to nucleic acid synthesis of an RNA or a DNAmolecule wherein the sequence of the newly synthesized strand of nucleicacid is dictated by the well-known rules of complementary base pairing(see, for example, Watson, 1987). Typically, vector mediatedmethodologies involve the introduction of the nucleic acid fragment intoa DNA or RNA vector, the clonal amplification of the vector, and therecovery of the amplified nucleic acid fragment. Examples of suchmethodologies are provided by U.S. Pat. No. 4,237,224, specificallyincorporated herein by reference in its entirety.

In another approach for the production of polypeptide variants of thepresent invention, recursive sequence recombination, as described inU.S. Pat. No. 5,837,458, may be employed. In this approach, iterativecycles of recombination and screening or selection are performed to“evolve” individual polynucleotide variants of the invention wherein oneor more desired activities is improved or modified.

In other embodiments of the present invention, the polynucleotidesequences provided herein can be advantageously used as probes orprimers for nucleic acid hybridization. As such, it is contemplated thatnucleic acid segments that comprise or consist of a sequence region ofat least about a 15 nucleotide long contiguous sequence that has thesame sequence as, or is complementary to, a 15 nucleotide longcontiguous sequence disclosed herein may be used. Longer contiguousidentical or complementary sequences, e.g., those of about 20, 30, 40,50, 100, 200, 500, 1000 (including all intermediate lengths) and even upto full length sequences will also be of use in certain embodiments.

Many template dependent processes are available to amplify a targetsequence of interest present in a sample. One of the best knownamplification methods is the polymerase chain reaction (PCR™) which isdescribed in detail in U.S. Pat. Nos. 4,683,195, 4,683,202 and4,800,159, each of which is incorporated herein by reference in itsentirety. Briefly, in PCR™, two primer sequences are prepared which arecomplementary to regions on opposite complementary strands of the targetsequence. An excess of deoxynucleoside triphosphates is added to areaction mixture along with a DNA polymerase (e.g., Taq polymerase). Ifthe target sequence is present in a sample, the primers will bind to thetarget and the polymerase will cause the primers to be extended alongthe target sequence by adding on nucleotides. By raising and loweringthe temperature of the reaction mixture, the extended primers willdissociate from the target to form reaction products, excess primerswill bind to the target and to the reaction product and the process isrepeated. Preferably reverse transcription and PCR™ amplificationprocedure may be performed in order to quantify the amount of mRNAamplified. Polymerase chain reaction methodologies are well known in theart.

Any of a number of other template dependent processes, many of which arevariations of the PCR™ amplification technique, are readily known andavailable in the art. Illustratively, some such methods include theligase chain reaction (referred to as LCR), described, for example, inEur. Pat. Appl. Publ. No. 320,308 and U.S. Pat. No. 4,883,750; QbetaReplicase, described in PCT Intl. Pat. Appl. Publ. No. PCT/US87/00880;Strand Displacement Amplification (SDA) and Repair Chain Reaction (RCR).Still other amplification methods are described in Great Britain Pat.Appl. No. 2 202 328, and in PCT Intl. Pat. Appl. Publ. No.PCT/US89/01025. Other nucleic acid amplification procedures includetranscription-based amplification systems (TAS) (PCT Intl. Pat. Appl.Publ. No. WO 88/10315), including nucleic acid sequence basedamplification (NASBA) and 3SR. Eur. Pat. Appl. Publ. No. 329,822describes a nucleic acid amplification process involving cyclicallysynthesizing single-stranded RNA (“ssRNA”), ssDNA, and double-strandedDNA (dsDNA). PCT Intl. Pat. Appl. Publ. No. WO 89/06700 describes anucleic acid sequence amplification scheme based on the hybridization ofa promoter/primer sequence to a target single-stranded DNA (“ssDNA”)followed by transcription of many RNA copies of the sequence. Otheramplification methods such as “RACE” (Frohman, 1990), and “one-sidedPCR” (Ohara, 1989) are also well-known to those of skill in the art.

As noted, the EBD fusion polynucleotides, polypeptides and vectors ofthe present invention are advantageous in the context of recombinantpolypeptide production, particularly where it is desired to achieve, forexample, improved solubility, improved yield, improved folding and/orreduced aggregation of a heterologous polypeptide to which an EBDpolypeptide sequence has been operably fused. Therefore, another aspectof the invention provides methods for producing a recombinant protein,for example by introducing into a host cell an expression vectorcomprising a polynucleotide sequence encoding a fusion polypeptide asdescribed herein, e.g., a fusion polypeptide comprising at least one EBDsequence and at least one heterologous polypeptide sequence of interest;and expressing the fusion polypeptide in the host cell. In a relatedembodiment, the method further comprises the step of isolating thefusion polypeptide from the host cell. In another embodiment, the methodfurther comprises the step of removing an EBD sequence from the fusionpolypeptide before or after isolating the fusion polypeptide from thehost cell.

For recombinant production of a fusion polypeptide of the invention, DNAsequences encoding the polypeptide components of a fusion polypeptide(e.g., one or more EBD sequences and a heterologous polypeptide sequenceof interest) may be assembled using conventional methodologies. In oneexample, the components may be assembled separately and ligated into anappropriate expression vector. For example, the 3′ end of the DNAsequence encoding one polypeptide component is ligated, with or withouta peptide linker, to the 5′ end of a DNA sequence encoding the secondpolypeptide component so that the reading frames of the sequences are inphase. This permits translation into a single fusion polypeptide thatretains the activities of both component polypeptides.

A peptide linker sequence may be employed to separate an EBD polypeptidesequence from a heterologous polypeptide sequence by some defineddistance, for example a distance sufficient to ensure that theadvantages of the invention are achieved, e.g., advantages such asimproved folding, reduced aggregation and/or improved yield. Such apeptide linker sequence may be incorporated into the fusion polypeptideusing standard techniques well known in the art. Suitable peptide linkersequences may be chosen based, for example, on the factors such as: (1)their ability to adopt a flexible extended conformation; and (2) theirinability to adopt a secondary structure that could interfere with theactivity of the EBD sequence. Illustrative peptide linker sequences, forexample, may contain Gly, Asn and Ser residues. Other near neutral aminoacids, such as Thr and Ala may also be used in the linker sequence.Amino acid sequences which may be usefully employed as linkers includethose disclosed in Maratea et al., Gene 40:39-46, 1985; Murphy et al.,Proc. Natl. Acad. Sci. USA 83:8258-8262, 1986; U.S. Pat. No. 4,935,233and U.S. Pat. No. 4,751,180. The linker sequence may generally be from 1to about 50 amino acids in length, for example.

The ligated DNA sequences of a fusion polynucleotide are operably linkedto suitable transcriptional and/or translational regulatory elements.The regulatory elements responsible for expression of DNA are locatedonly 5′ to the DNA sequence encoding the first polypeptides. Similarly,stop codons required to end translation and transcription terminationsignals are only present 3′ to the DNA sequence encoding the secondpolypeptide.

The EBD and heterologous polynucleotide sequences may comprise asequence as described herein, or may comprise a sequence that has beenmodified to facilitate recombinant polypeptide production. As will beunderstood by those of skill in the art, it may be advantageous in someinstances to produce polypeptide-encoding polynucleotide sequencespossessing non-naturally occurring codons. For example, codons preferredby a particular prokaryotic or eukaryotic host can be selected toincrease the rate of protein expression or to produce a recombinant RNAtranscript having desirable properties, such as a half-life which islonger than that of a transcript generated from the naturally occurringsequence.

Moreover, the polynucleotide sequences of the present invention can beengineered using methods generally known in the art in order to alterpolypeptide encoding sequences for a variety of reasons, including butnot limited to, alterations which modify the cloning, processing, and/orexpression of the gene product. For example, DNA shuffling by randomfragmentation and PCR reassembly of gene fragments and syntheticoligonucleotides may be used to engineer the nucleotide sequences. Inaddition, site-directed mutagenesis may be used to insert newrestriction sites, alter glycosylation patterns, change codonpreference, produce splice variants, or introduce mutations, and soforth.

In a particular embodiment, a fusion polynucleotide is engineered tofurther comprise a cleavage site located between the EBDpolypeptide-encoding sequence and the heterologous polypeptide sequence,so that the heterologous polypeptide may be cleaved and purified awayfrom an EBD polypeptide sequence at any desired stage followingexpression of the fusion polypeptide. Illustratively, a fusionpolynucleotide of the invention may be designed to include heparin,thrombin, or factor Xa protease cleavage sites.

In order to express a desired polypeptide, the nucleotide sequencesencoding the polypeptide, or functional equivalents, may be insertedinto appropriate expression vector, i.e., a vector which contains thenecessary elements for the transcription and translation of an insertedcoding sequence. Methods which are well known to those skilled in theart may be used to construct expression vectors containing sequencesencoding a polypeptide of interest and appropriate transcriptional andtranslational control elements. These methods include in vitrorecombinant DNA techniques, synthetic techniques, and in vivo geneticrecombination. Such techniques are described, for example, in Sambrook,J. et al. (1989) Molecular Cloning, A Laboratory Manual, Cold SpringHarbor Press, Plainview, N.Y., and Ausubel, F. M. et al., (1989) CurrentProtocols in Molecular Biology, John Wiley & Sons, New York. N.Y.

A variety of expression vector/host systems may be utilized to containand express polynucleotide sequences of the present invention. Theseinclude, but are not limited to, microorganisms such as bacteriatransformed with recombinant bacteriophage, plasmid, or cosmid DNAexpression vectors; yeast transformed with yeast expression vectors;insect cell systems infected with virus expression vectors (e.g.,baculovirus); plant cell systems transformed with virus expressionvectors (e.g., cauliflower mosaic virus, CaMV; tobacco mosaic virus,TMV) or with bacterial expression vectors (e.g., Ti or pBR322 plasmids);or animal cell systems.

The “control elements” or “regulatory sequences” present in anexpression vector are those non-translated regions of thevector—enhancers, promoters, 5′ and 3′ untranslated regions—whichinteract with host cellular proteins to carry out transcription andtranslation. Such elements may vary in their strength and specificity.Depending on the vector system and host utilized, any number of suitabletranscription and translation elements, including constitutive andinducible promoters, may be used. For example, when cloning in bacterialsystems, inducible promoters such as the hybrid lacZ promoter of thepBLUESCRIPT phagemid (Stratagene, La Jolla, Calif.) or pSPORT1 plasmid(Gibco BRL, Gaithersburg, Md.) and the like may be used. In mammaliancell systems, promoters from mammalian genes or from mammalian virusesare generally preferred. If it is necessary to generate a cell line thatcontains multiple copies of the sequence encoding a polypeptide, vectorsbased on SV40 or EBV may be advantageously used with an appropriateselectable marker.

In bacterial systems, any of a number of expression vectors may beselected depending upon the use intended for the expressed polypeptide.For example, when large quantities are needed, for example for theinduction of antibodies, vectors which direct high level expression offusion proteins that are readily purified may be used. Such vectorsinclude, but are not limited to, the multifunctional E. coli cloning andexpression vectors such as pBLUESCRIPT (Stratagene), in which thesequence encoding the polypeptide of interest may be ligated into thevector in frame with sequences for the amino-terminal Met and thesubsequent 7 residues of β-galactosidase so that a hybrid protein isproduced; pIN vectors (Van Heeke, G. and S. M. Schuster (1989) J. Biol.Chem. 264:5503-5509); and the like. Proteins made in such systems may bedesigned to include heparin, thrombin, or factor Xa protease cleavagesites so that the cloned polypeptide of interest can be released fromthe EBD moiety at will.

In the yeast, Saccharomyces cerevisiae, a number of vectors containingconstitutive or inducible promoters such as alpha factor, alcoholoxidase, and PGH may be used. For reviews, see Ausubel et al. (supra)and Grant et al. (1987) Methods Enzymol. 153:516-544.

In cases where plant expression vectors are used, the expression ofsequences encoding polypeptides may be driven by any of a number ofpromoters. For example, viral promoters such as the 35S and 19Spromoters of CaMV may be used alone or in combination with the omegaleader sequence from TMV (Takamatsu, N. (1987) EMBO J. 6:307-311.Alternatively, plant promoters such as the small subunit of RUBISCO orheat shock promoters may be used (Coruzzi, G. et al. (1984) EMBO J.3:1671-1680; Broglie, R. et al. (1984) Science 224:838-843; and Winter,J. et al. (1991) Results Probl. Cell Differ. 17:85-105). Theseconstructs can be introduced into plant cells by direct DNAtransformation or pathogen-mediated transfection. Such techniques aredescribed in a number of generally available reviews (see, for example,Hobbs, S. or Murry, L. E. in McGraw Hill Yearbook of Science andTechnology (1992) McGraw Hill, New York, N.Y.; pp. 191-196).

An insect system may also be used to express a polypeptide of interest.For example, in one such system, Autographa californica nuclearpolyhedrosis virus (AcNPV) is used as a vector to express foreign genesin Spodoptera frugiperda cells or in Trichoplusia larvae. The sequencesencoding the polypeptide may be cloned into a non-essential region ofthe virus, such as the polyhedrin gene, and placed under control of thepolyhedrin promoter. Successful insertion of the polypeptide-encodingsequence will render the polyhedrin gene inactive and producerecombinant virus lacking coat protein. The recombinant viruses may thenbe used to infect, for example, S. frugiperda cells or Trichoplusialarvae in which the polypeptide of interest may be expressed (Engelhard,E. K. et al. (1994) Proc. Natl. Acad. Sci. 91:3224-3227).

In mammalian host cells, a number of viral-based expression systems aregenerally available. For example, in cases where an adenovirus is usedas an expression vector, sequences encoding a polypeptide of interestmay be ligated into an adenovirus transcription/translation complexconsisting of the late promoter and tripartite leader sequence.Insertion in a non-essential E1 or E3 region of the viral genome may beused to obtain a viable virus which is capable of expressing thepolypeptide in infected host cells (Logan, J. and Shenk, T. (1984) Proc.Natl. Acad. Sci. 81:3655-3659). In addition, transcription enhancers,such as the Rous sarcoma virus (RSV) enhancer, may be used to increaseexpression in mammalian host cells.

Specific initiation signals may also be used to achieve more efficienttranslation of sequences encoding a polypeptide of interest. Suchsignals include the ATG initiation codon and adjacent sequences. Incases where sequences encoding the polypeptide, its initiation codon,and upstream sequences are inserted into the appropriate expressionvector, no additional transcriptional or translational control signalsmay be needed. However, in cases where only coding sequence, or aportion thereof, is inserted, exogenous translational control signalsincluding the ATG initiation codon should be provided. Furthermore, theinitiation codon should be in the correct reading frame to ensuretranslation of the entire insert. Exogenous translational elements andinitiation codons may be of various origins, both natural and synthetic.The efficiency of expression may be enhanced by the inclusion ofenhancers which are appropriate for the particular cell system which isused, such as those described in the literature (Scharf, D. et al.(1994) Results Probl. Cell Differ. 20:125-162).

In addition, a host cell strain may be chosen for its ability tomodulate the expression of the inserted sequences or to process theexpressed protein in the desired fashion. Such modifications of thepolypeptide include, but are not limited to, acetylation, carboxylation,glycosylation, phosphorylation, lipidation, and acylation.Post-translational processing which cleaves a “prepro” form of theprotein may also be used to facilitate correct insertion, folding and/orfunction. Different host cells such as CHO, COS, HeLa, MDCK, HEK293, andWI38, which have specific cellular machinery and characteristicmechanisms for such post-translational activities, may be chosen toensure the correct modification and processing of the foreign protein.

For long-term, high-yield production of recombinant proteins, stableexpression is generally preferred. For example, cell lines which stablyexpress a polynucleotide of interest may be transformed using expressionvectors which may contain viral origins of replication and/or endogenousexpression elements and a selectable marker gene on the same or on aseparate vector. Following the introduction of the vector, cells may beallowed to grow for 1-2 days in an enriched media before they areswitched to selective media. The purpose of the selectable marker is toconfer resistance to selection, and its presence allows growth andrecovery of cells which successfully express the introduced sequences.Resistant clones of stably transformed cells may be proliferated usingtissue culture techniques appropriate to the cell type.

Any number of selection systems may be used to recover transformed celllines. These include, but are not limited to, the herpes simplex virusthymidine kinase (Wigler, M. et al. (1977) Cell 11:223-32) and adeninephosphoribosyltransferase (Lowy, I. et al. (1990) Cell 22:817-23) geneswhich can be employed in tk.sup.− or aprt.sup.− cells, respectively.Also, antimetabolite, antibiotic or herbicide resistance can be used asthe basis for selection; for example, dhfr which confers resistance tomethotrexate (Wigler, M. et al. (1980) Proc. Natl. Acad. Sci.77:3567-70); npt, which confers resistance to the aminoglycosides,neomycin and G-418 (Colbere-Garapin, F. et al (1981) J. Mol. Biol.150:1-14); and als or pat, which confer resistance to chlorsulfuron andphosphinotricin acetyltransferase, respectively (Murry, supra).Additional selectable genes have been described, for example, trpB,which allows cells to utilize indole in place of tryptophan, or hisD,which allows cells to utilize histinol in place of histidine (Hartman,S.C. and R. C. Mulligan (1988) Proc. Natl. Acad. Sci. 85:8047-51). Theuse of visible markers has gained popularity with such markers asanthocyanins, β-glucuronidase and its substrate GUS, and luciferase andits substrate luciferin, being widely used not only to identifytransformants, but also to quantify the amount of transient or stableprotein expression attributable to a specific vector system (Rhodes, C.A. et al. (1995) Methods Mol. Biol. 55:121-131).

Although the presence/absence of marker gene expression suggests thatthe gene of interest is also present, its presence and expression mayneed to be confirmed. For example, if the sequence encoding apolypeptide is inserted within a marker gene sequence, recombinant cellscontaining sequences can be identified by the absence of marker genefunction. Alternatively, a marker gene can be placed in tandem with apolypeptide-encoding sequence under the control of a single promoter.Expression of the marker gene in response to induction or selectionusually indicates expression of the tandem gene as well.

Alternatively, host cells that contain and express a desiredpolynucleotide sequence may be identified by a variety of proceduresknown to those of skill in the art. These procedures include, but arenot limited to, DNA-DNA or DNA-RNA hybridizations and protein bioassayor immunoassay techniques which include, for example, membrane,solution, or chip based technologies for the detection and/orquantification of nucleic acid or protein.

A variety of protocols for detecting and measuring the expression ofpolynucleotide-encoded products, using either polyclonal or monoclonalantibodies specific for the product are known in the art. Examplesinclude enzyme-linked immunosorbent assay (ELISA), radioimmunoassay(RIA), and fluorescence activated cell sorting (FACS). A two-site,monoclonal-based immunoassay utilizing monoclonal antibodies reactive totwo non-interfering epitopes on a given polypeptide may be preferred forsome applications, but a competitive binding assay may also be employed.These and other assays are described, among other places, in Hampton, R.et al., (1990; Serological Methods, a Laboratory Manual, APS Press, StPaul. Minn.) and Maddox, D. E. et al. (1983; J. Exp. Med.158:1211-1216).

A wide variety of labels and conjugation techniques are known by thoseskilled in the art and may be used in various nucleic acid and aminoacid assays. Means for producing labeled hybridization or PCR probes fordetecting sequences related to polynucleotides include oligolabeling,nick translation, end-labeling or PCR amplification using a labelednucleotide. Alternatively, the sequences, or any portions thereof may becloned into a vector for the production of an mRNA probe. Such vectorsare known in the art, are commercially available, and may be used tosynthesize RNA probes in vitro by addition of an appropriate RNApolymerase such as T7, T3, or SP6 and labeled nucleotides. Theseprocedures may be conducted using a variety of commercially availablekits. Suitable reporter molecules or labels, which may be used includeradionuclides, enzymes, fluorescent, chemiluminescent, or chromogenicagents as well as substrates, cofactors, inhibitors, magnetic particles,and the like.

Host cells transformed with a polynucleotide sequence of interest may becultured under conditions suitable for the expression and recovery ofthe polypeptide from cell culture. The polypeptide produced by arecombinant cell may be secreted or contained intracellularly dependingon the sequence and/or the vector used. As will be understood by thoseof skill in the art, expression vectors containing polynucleotides ofthe invention may be designed to contain signal sequences which directsecretion of the encoded polypeptide through a prokaryotic or eukaryoticcell membrane. Other recombinant constructions may be used to joinsequences encoding a polypeptide of interest to polynucleotide sequenceencoding a polypeptide domain which will facilitate purification ofsoluble proteins. Such purification facilitating domains include, butare not limited to, metal chelating peptides such ashistidine-tryptophan modules that allow purification on immobilizedmetals, protein A domains that allow purification on immobilizedimmunoglobulin, and the domain utilized in the FLAGS extension/affinitypurification system (Immunex Corp., Seattle, Wash.). The inclusion ofcleavable linker sequences such as those specific for Factor Xa orenterokinase (Invitrogen. San Diego, Calif.) between the purificationdomain and the encoded polypeptide may be used to facilitatepurification. One such expression vector provides for expression of afusion protein containing a polypeptide of interest and a nucleic acidencoding 6 histidine residues preceding a thioredoxin or an enterokinasecleavage site. The histidine residues facilitate purification on IMIAC(immobilized metal ion affinity chromatography) as described in Porath,J. et al. (1992, Prot. Exp. Purif. 3:263-281) while the enterokinasecleavage site provides a means for purifying the desired polypeptidefrom the fusion protein. Further discussion of vectors which comprisefusion proteins can be found in Kroll, D. J. et al. (1993; DNA CellBiol. 12:441-453).

In addition to recombinant production methods, polypeptides of theinvention, and fragments thereof, may be produced by direct peptidesynthesis using solid-phase techniques (Merrifield J. (1963) J. Am.Chem. Soc. 85:2149-2154). Polypeptide synthesis may be performed usingmanual techniques or by automation. Automated synthesis may be achieved,for example, using Applied Biosystems 431A Peptide Synthesizer (PerkinElmer). Alternatively, various fragments may be chemically synthesizedseparately and combined using chemical methods to produce the fulllength molecule.

According to another aspect, the present invention further providesbinding agents, such as antibodies and antigen-binding fragmentsthereof, that specifically bind to an EBD sequence according to thepresent invention, or to a portion, variant or derivative thereof. Suchbinding agents may be used, for example, to detect the presence of apolypeptide comprising an EBD sequence, to facilitate purification of apolypeptide comprising an EBD sequence, and the like. An antibody, orantigen-binding fragment thereof, is said to “specifically bind” to apolypeptide if it reacts at a detectable level (within, for example, anELISA assay) with the polypeptide, and does not react detectably withunrelated polypeptides under similar conditions.

Antibodies and other binding agents can be prepared using conventionalmethodologies. For example, monoclonal antibodies specific for apolypeptide of interest may be prepared using the technique of Kohlerand Milstein, Eur. J. Immunol. 6:511-519, 1976, and improvementsthereto. Briefly, these methods involve the preparation of immortal celllines capable of producing antibodies having the desired specificity(i.e., reactivity with the polypeptide of interest). Such cell lines maybe produced, for example, from spleen cells obtained from an animalimmunized as described above. The spleen cells are then immortalized by,for example, fusion with a myeloma cell fusion partner, preferably onethat is syngeneic with the immunized animal. A variety of fusiontechniques may be employed. For example, the spleen cells and myelomacells may be combined with a nonionic detergent for a few minutes andthen plated at low density on a selective medium that supports thegrowth of hybrid cells, but not myeloma cells. A preferred selectiontechnique uses HAT (hypoxanthine, aminopterin, thymidine) selection.After a sufficient time, usually about 1 to 2 weeks, colonies of hybridsare observed. Single colonies are selected and their culturesupernatants tested for binding activity against the polypeptide.Hybridomas having high reactivity and specificity are preferred.

Monoclonal antibodies may be isolated from the supernatants of growinghybridoma colonies. In addition, various techniques may be employed toenhance the yield, such as injection of the hybridoma cell line into theperitoneal cavity of a suitable vertebrate host, such as a mouse.Monoclonal antibodies may then be harvested from the ascites fluid orthe blood. Contaminants may be removed from the antibodies byconventional techniques, such as chromatography, gel filtration,precipitation, and extraction. The polypeptides of this invention may beused in the purification process in, for example, an affinitychromatography step.

A number of “humanized” antibody molecules comprising an antigen-bindingsite derived from a non-human immunoglobulin have been described,including chimeric antibodies having rodent V regions and theirassociated CDRs fused to human constant domains (Winter et al. (1991)Nature 349:293-299; Lobuglio et al. (1989) Proc. Nat. Acad. Sci. USA86:4220-4224; Shaw et al. (1987) J Immunol. 138:4534-4538; and Brown etal. (1987) Cancer Res. 47:3577-3583), rodent CDRs grafted into a humansupporting FR prior to fusion with an appropriate human antibodyconstant domain (Riechmann et al. (1988) Nature 332:323-327; Verhoeyenet al., (1988) Science 239:1534-1536; and Jones et al. (1986) Nature321:522-525), and rodent CDRs supported by recombinantly veneered rodentFRs (European Patent Publication No. 519,596, published Dec. 23, 1992).These “humanized” molecules are designed to minimize unwantedimmunological response toward rodent antihuman antibody molecules whichlimits the duration and effectiveness of therapeutic applications ofthose moieties in human recipients.

Yet another aspect of the invention provides kits comprising one or morecompositions described herein, e.g., an isolated EBD polynucleotide,polypeptide, antibody, vector, host cell, etc. In a particularembodiment, the invention provides a kit containing an expression vectorcomprising a polynucleotide sequence encoding an EBD polypeptidesequence and a multiple cloning site for easily introducing into thevector a polynucleotide sequence encoding a heterologous polypeptidesequence of interest. In another embodiment, the expression vectorfurther comprises an engineered cleavage site to facilitate separationof the EBD polypeptide sequence from the heterologous polypeptidesequence of interest following recombinant production.

The following Examples are offered by way of illustration and not by wayof limitation.

EXAMPLES Example 1 Artificial EBDs Effectively Solubilize InsolubleProteins

To address host cell toxicity problems associated with the use ofcertain naturally-occurring EBD sequences in fusion with heterologousproteins, artificial sequences were designed. Our knowledge of theintrinsic protein disorder phenomenon allowed us to design highlydisordered artificial EBD sequences with desirable charge properties.Further, the likelihood that a completely artificial sequence wouldpossess cytotoxicity due to the specific interaction with cellularcomponents seemed to be minimal.

Designing the Artificial Entropic Bristles

In order to serve as an artificial EBD, a polypeptide chain should behighly flexible and disordered. Statistical comparisons of amino acidcompositions indicated that disordered and ordered regions in proteinsare different to a significant degree. Based on the analysis ofintrinsically disordered (ID) proteins and disordered regions withinproteins, amino acid residues were categorized as (1) order-promoting,(2) disorder-promoting and (3) neutral (Dunker, et al., J Mol GraphModel, 2001. 19(1): p. 26-59). FIG. 1 presents relative amino acidcompositions of ID regions available in the DisProt database (Sickmeieret al. Bioinformatics, 2005. 21(1): p. 137-40). The amino acidcompositions were compared using a profiling approach (Dunker, et al., JMol Graph Model, 2001. 19(1): p. 26-59). FIG. 1 shows that certainorder-promoting residues include C, W, Y, I, F, V, L, H, T, and N,disorder-promoting residues include D, M, K, R, S, Q, P, E, and G, whileneutral residues include A. It is notable that H, T, N, G, and D areborderline by the 0.1 fractional difference criterion, and so theseresidues could also be considered neutral in certain contexts.

The right-most bars representing the most disorder-promoting residues(E, P, Q, S, and K) together with the disorder-neutral residue G werechosen as basis for the de novo design of artificial EBDs. An artificialEBD was designed to contain the chosen residues in about the followingamino acid ratios: X:P:Q:S=1:2:1:2, where X is a variable position togenerate positive, negative or neutral bristles, and corresponds to oneof K, E, or G, respectively.

The 1:2:1:2 proportions for X:P:Q:S were based on the followingobservations. Proline disrupts secondary structure (except forpolyproline II helix) and contains hydrophobic surfaces for weak bindingto possible aggregation patches, so a high proportion of P was chosen.PolyQ spontaneously aggregates, so a low proportion of Q was chosen toavoid aggregation-prone continuous stretches of Q. The side chain ofserine is hydrophilic, but its ability to hydrogen bond with thebackbone leads to very high conformational variability, so a highproportion of S was chosen. Since structured regions of proteins nevercontain long regions of very low complexity (Romero et al., Proteins.2001. 42(1): p. 38-48), a small number of different amino acids (e.g., alow complexity bristle) reduces the chance of accidental formation ofstable tertiary structure by stable interactions with other parts of theprotein.

Based on these prerequisites, a 100 residue long random sequence wasgenerated. The resulting sequence is shown in FIG. 2. Then, a fragmentof this sequence, underlined sequence in FIG. 2A, was chosen to serve asthe de novo EBD. This general sequence was used to generate EBDs thatwere positive (EB+), negative (EB−) and neutral (EB0) (FIG. 2B).

Target Protein Selection

Thirteen proteins previously shown to be insoluble without fusions orshown to be insoluble even when fused to maltose-binding protein (MBP)were selected (Kapust et al., Protein Sci, 1999. 8(8): p. 1668-74;Kataeva et al., J Proteome Res, 2005. 4(6): p. 1942-51). Nine of theseproteins were insoluble even at 30° C. of induction (Kataeva et al., JProteome Res, 2005. 4(6): p. 1942-51). The proteins had molecular massesfrom 8.4 to 28.3 kDa; isoelectric points (pI) from 3.55 to 10.9, and netcharges from +20 to −17. These proteins and some of their properties arelisted in Table 2.

Cloning Methods

To attach EBDs to N-termini of target proteins, the Gateway CloningTechnique (Invitrogen) based on a specific recombination of homologousDNA sequences was used. For polymerase chain reaction (PCR) accuracy,the high fidelity and specificity AccuPrime Pfx DNA polymerase(Invitrogen) was used (Takagi et al., Appl Environ Microbiol, 1997.63(11): p. 4504-10). Primers were designed and optimized using XPressionPrimer 3.0 software. PCR products were purified using Wizard SV Gel andPCR Clean-Up System (Promega) or by mini-dialysis using Millipore. Togenerate entry clones, pDONR221 (Invitrogen) was used as an entryvector. All entry clones have been verified by sequencing. For thecreation of expression clones, pDEST-42 destination vector (Gateway) wasused. A point point mutation in pDEST-42 was done using QuickChange IIXL Site-Directed Mutagenesis Kit (Stratagene). One Shot TOP10 and BL21Star (DE3) One Shot competent cells (Invitrogen) were commonly used fortransformation with BP and LR reactions, respectively. Plasmid DNAs werepurified using Wizard Plus SV Minipreps DNA Purufication System(Promega). To create maltose-binding protein (MBP) fusions the targetgenes were amplified by PCR using forward and reverse primers flanked byattB1 and attB2 sites, respectively, and cloned into entry vector asdescribed above. To create expression clones, pDEST-544 vector(Invitrogen) was used. Proteins expressed from this vector had an MBP attheir N-termini.

Cell Growth and Lysis

Cultures were grown in an LB medium supplied with 100 μg/mL ampicillinat 37° C. overnight and used next morning to start new 1 ml cultures.The tubes were incubated with shaking at 37° C. for 4 hours. Then IPTGwas added to a final concentration of 1 mM and the tubes were shaken foradditional 4 h at either 37° C. or 30° C. The cells were collected bycentrifugation and lysed chemically using the combination of mildnonionic detergent and a lysozyme (B-PER Reagent, Thermo). Thesuspensions were stirred for 30 min at room temperature. The lysedsolution was designated as a “whole fraction”. The “soluble fraction”was obtained by removal of insoluble fraction by centrifugation. Thewhole and the soluble fractions were used for the detection of proteinexpression and solubility, respectively.

Design of Cloning Strategy

To avoid translation of the eleven amino acid residues attB1recombination site, (i.e. for native protein expression), its startcodon (ATG) was mutated to ATA encoding isoleucine. For the same reason,Shine-Dalgarno (SD) sequence followed by a linker (L) and a start codonwere inserted between the attB1 site and the entropic bristle sequence.Original reversed transcripts of 30 amino acid residues of the designedartificial EBDs were 90 bases long. After addition of a 5′-fragment (theattB1 site, the Shine Dalgarno, the linker, and the start codon), theresulted DNA fragment to be synthesized was over 140 bases long. Tominimize mistakes upon synthesis of such a large DNA fragment, theputative DNA sequence of each EBD was divided into three pieces. Eachpiece was amplified and linked to the next one using set of PCRs andoverlapping primers (see FIG. 3) (Kataeva et al., J Proteome Res, 2005.4(6): p. 1942-51). After generating of EBD DNA fragments, target geneswith a stop codons at their 3′-termini were amplified by PCR and linkedto the 3′-terminus of each entropic bristle using the above principle(FIG. 3). Thus, each final PCR product had the following composition:attB1-SD-L-EBD-Target Gene-stop-attB2. The constructs were inserted intocloning vector. Plasmid DNAs of the clones were isolated and verified bysequencing. The “right” clones were used (1) as sources of DNA sequencesencoding EBDs and (2) to make expression clones in LR reaction.

Expression and Solubility Test

To evaluate protein expression and solubility, the proteins of the wholeand soluble fractions were separated by SDS-PAGE using NuPAGE 4-12%Bis-Tris Gels and the supplied reagents (Invitrogen). Gels were stainedwith Coomassie Blue Reagent.

Results: Expression and Solubility of Fusion Proteins ComprisingArtificial EBDs

FIG. 4 and Table 2 show that artificial EBDs fused to the N-termini oftarget proteins was highly effective. Eleven out of thirteen insolubleproteins were solubilized by this approach (Highlighted portions ofTable 2 represent the proteins that were solubilized by fusion toartificial EBDs or to MBP). The level of expression of all EBD-fusionswas good. At 37° C. of induction, neutral EB0 solubilized 1 protein.Charged EB+ and EB− solubilized 5 and 6 proteins, respectively.Decreasing induction temperature improved soluble protein expression(Kataeva et al., J Proteome Res, 2005. 4(6): p. 1942-51). Induction at30° C. did not change solubility of EBDO fusions but resulted in 4 and 1more soluble EBD+ and EBD− fusion proteins, respectively. FIG. 4illustrates expression and solubility of 10 bacterial proteins fusedeither to artificial EBDs (FIG. 4A) or to maltose-binding protein (FIG.4B), whereas Table 2 summarizes the results of the solubility studies.

TABLE 2 37° C. 30° C. 37° C. 30° C. MW EBD₊ EBD⁻ EBD₀ EBD₊ EBD⁻ EBD₀ MBPfusion Protein (kDa) pI Charge E S E S E S E S E S E S E S E S342-Transposase_mut 23.3 10.9 20 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 01981-IF-2B 17.1 10 6.5 1 0 1 1 1 0 1 0 1 1 1 0 1 0 1 0 2516-DUF199 9.29.55 3 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 758-DUF111 12.5 7.3 5 1 1 1 1 1 01 1 1 1 1 0 1 0 1 0 2843-Cons_hypoth95 21.7 6.8 0.5 1 1 1 1 1 1 1 1 1 11 1 1 1 1 1 408-UbiA 12.4 5.8 −0.5 1 1 1 1 1 0 1 1 1 1 1 0 1 0 1 02384-HD 21.1 5.5 −1.5 1 0 1 0 1 0 1 1 1 1 1 0 1 1 1 1 CATΔ9 26.7 5.2 −141 0 1 1 0 0 1 1 1 0 0 0 1 0 1 0 2141-DNA_gyraseB_C 23.2 5.2 −3 1 1 1 0 10 1 1 1 0 1 0 1 0 0 0 GFP 28.3 5.13 −14 1 0 1 0 1 0 1 1 1 1 0 0 1 1 1 1p16 17.7 4.94 −5 1 0 1 0 1 0 1 1 1 0 0 0 1 0 1 0 1653-UPF0004 17.1 4.4−8.5 1 1 1 0 1 0 1 1 1 0 1 0 1 1 1 1 1439-AAA_div 8.4 3.55 −17 1 0 1 1 10 1 0 1 1 1 0 1 0 1 0 E = expression; S = solubilization; 1 = soluble; 0= insoluble

In summary, fusion of MBP significantly increased the solubility of just4 of 13 proteins, at 37° C. or at 30° C., whereas the artificial EBD ofthe present invention increased the solubility for 11 of the 13previously insoluble proteins.

Example 2 Development of Novel EBD-Fusion Expression Vectors

A. Design of the AquoProt/AquoKin Vector Backbone

This example describes the cloning of the generic 4.2 kilobase pAquoProtand pAquoKin vector backbone. pUC19 is the source for the dsDNApolypeptide used to build the AquoProt and AquoKin vectors. Functionalfeatures already present in the pUC19 vector include the DNA sequenceencoding ampicillin resistance and the E. coli high copy origin.Additional features in the hybrid plasmid include an f1 origin, allowingfor in vitro translation system compatibility; a novelcloning/expression cassette allowing for expression of a uniquesynthetic polypeptide fusion to a target protein (described in detailbelow); and the LacI gene enabling host-independent control of thepromoter controlling protein translation within the E. coli. Digestionof the pUC19 vector with the EcoO1091 restriction enzyme allowedligation of the f1 origene fragment in an anti-sense orientation. Next,the pUC19 vector containing antisense f1-origin was digested with NdeIand PvuII restriction enzymes to allow for the directional insertion ofthe synthesized cloning/expression cassette described below. This stepwas completed prior to the insertion of the LacI gene due to thepresence of PvuII sites in the LacI gene coding sequence. The pUC19vector containing antisense f1-origin and the cloning/expressioncassette was digested using the SapI restriction site, and LacI wasligated in a sense orientation. The resultant product of these cloningsteps is shown in FIG. 5, and is termed the pAquoProt vector backbone.In addition, the cloning/expression cassette can be partially replacedby digestion at SalI and NdeI sites followed by ligation of the AquoKinexpression cassette to yield the pAquoKin vector backbone.

B. Design of the AquoProt Cloning/Expression Cassette.

This example describes the functional features designed into the 378 bpcloning/expression cassette that will result in the pAquoProt vector(FIG. 6). Preceding 5′ to 3′ from the ribosomal binding site (AAGAG,start by 100) several features were added to distinguish this cloningregion from the original pUC19 vector. The DNA fragment for anN-terminal poly-histidine (His-tag) preceded by a start codon wasinserted to aid purification and detection. Downstream of the His-tag aunique BstBI restriction site (start by 144) was added. Cleavage of theBstBI site was utilized for the in-frame insertion of the artificialfusion sequences described. A DNA fragment encoding the recognitionsequence for the endopeptidase, enterokinase, follows the BstBI andfacilitates post-translational cleavage of the His-tag andfusion-peptide. This accommodates end-user needs to remove fusionpolypeptides as applications dictate. Next the unique restriction sitesBamHI, MfeI, EcoRV, KpnI, HindIII, Eag1, NotI, XhoI are present toassist cloning of the desired protein encoding cDNA into the vector.Finally, a C-terminal HA-tag encoding sequence (start by 224) exists sothat the hybrid polypeptide can be post-translationally detected viaimmunochemistry. Alternatively, a stop codon can be placed as the finalcodon of the user-inserted protein polypeptide to prevent the additionof the post-translational addition of the HA-tag.

C. Design of the AquoKin Expression/Cloning Cassette

This example describes the functional features designed into the 381 bpcloning/expression cassette that distinguish the pAquokin vector (FIG.7) from the pAquoProt vector (FIG. 6). First, a second solubility-aidingpolypeptide described within claims X-Z will be cloned into the Eco47IIIsite (start bp247). This restriction site is downstream of theC-terminal affinity tag, and results in the translation of a hybriduser-inserted protein with N- and C-terminal solubility-aiding EBDfusions. The vector has been designed such that these fusions can besimultaneously removed by post-translational digestion with theendopeptidase, enterokinase. To facilitate the one-step cleavage of bothfusions the C-terminal affinity tag was changed from an HA-tag to theFLAG™-tag recognition sequence (U.S. Pat. No. 4,703,004) which alsoencodes the enterokinase consensus site. The resultantpost-translational cleavage product will be the user-inserted proteinsequence with a c-terminal DYKDDDK sequence that allows detection of thehybrid-polypeptide via immunochemistry.

Example 3 Artificial EBDs Effectively Solubilize Insoluble Proteins

Example 1 demonstrated that the 30 amino acid negatively charged EBDswere more effective in some instances than the neutral and positiveEBDs. Therefore, additional negatively charged artificial EBDs weredesigned to expand the range of synthetic fusion tags. These furtherEBDs contain amino acids in the following approximate ratios:E:P:Q:S=1:2:1:1, E:P:Q:S=1:4:1:1, E:P:Q:S=2:2:1:1; E:P:Q:G=1:4:1:1,E:P:Q:G=2:2:1:1, E:P:Q:G=3:2:1:1, D:E:P:Q:S:G=1:2:3:1:2:1, and theD:E:P:Q:S:G=1:2:3:1:2:1 EBD sequence was also modified to contain thehydrophobic patches comprised of amino acids I, L, M, F, and V such thatthe EBD had approximately 12% overall hydrophobic character. Based onthese amino acid ratios, 120 to 250 residue long sequences weregenerated computationally. The resulting polypeptide sequences arerepresented as SEQ ID NOs: 38-45. The EBD amino acid sequences werereverse translated into polynucleotide open reading frames andsynthesized de novo (SEQ ID NOs: 46-53). The polynucleotide sequenceswere utilized as templates to generate novel EBDs of differing lengthsand amino acid compositions. Once PCR amplified, the novel EBD codingsequences were cloned into the BstBI site of the pAquoProt vectorbackbone such that target proteins expressed from these plasmids have anN-terminal fusion consisting of a His-tag-EBD-EK cleavage site.Likewise, novel EBD coding sequences were cloned in various combinationsinto the BstBI site and Eco47III site of the pAquoKin vector backbonesuch that a heterologous protein expressed from this plasmid has EBDstranslationally fused to both termini. A large library of expressionvectors was generated by combining various EBDs into generic expressionvectors to further evaluate the physical properties that areadvantageous for promoting the soluble expression of a fusion partner.Table 3 lists a subset of the EBDs that have been tested and theirphysical properties. These EBDs span a range of lengths (24 to 250 aminoacids) and exhibit a variety of amino acid compositions. Regardless ofthe sequence diversity between individual EBDs, all of these EBDs arelow complexity, unstructured, synthetic fusion tags with negative netcharges.

TABLE 3 Seq ID (A.A. #s) Parent A.A. ratio EBD length MW Net Charge plSeqID 7 (96-120) E:P:Q:G = 1:4:1:1 24 2.5 kDa −6 3.63 SeqID 5 (61-120)E:P:Q:S = 2:2:1:1 60 6.8 kDa −24 3.08 SeqID 9 (1-60) E:P:Q:G = 2:2:1:160 6.3 kDa −18 3.09 SeqID 11 (1-60) E:P:Q:G = 3:2:1:1 60 6.7 kDa −252.97 SeqID 9 (47-120) E:P:Q:G = 2:2:1:1 74 7.9 kDa −23 3.10 SeqID 11(1-120) E:P:Q:G = 3:2:1:1 120 13.1 kDa  −51 2.75 SeqID 13 (1-144)D:E:P:Q:S:G = 144  15 kDa −41 2.69 1:2:3:1:2:1 SeqID 15 (1-250) SeqID13 + I, L, 250 26.1 kDa  −65 2.48 M, F V SeqID 15 (1-81) SeqID 13 + I,L, 81 8.8 kDa −27 2.87 M, F VEBD Performance Testing

Various insoluble target proteins were selected to test thesolubility-enhancing performance of the EBDs. cDNA clones for therecalcitrant proteins were either purchased from commercial sources orobtained elsewhere. The coding region for each target protein wasamplified by PCR with the high fidelity AccuPrime Pfx DNA polymerase(Invitrogen) from their respective cDNA clones using primers designedfor use with the In-Fusion Advantage PCR cloning kit (Clontech). Thevarious EBD-containing expression plasmids were digested with therestriction enzyme BamHI and gel purified. The target gene PCR productswere then cloned into the expression vectors at the BamHI restrictionsite following the standard In-fusion cloning protocol from Clontech.Following the cloning reactions chemically competent Acella cells(EdgeBio) were used for transformation.

Cell Growth and Lysis

Cultures were grown in LB medium supplied with 100 μg/mL ampicillin at37° C. overnight. The following morning 150 μL of culture was pelleted,raised in fresh medium and added to start a 3 mL culture. The culturetubes were incubated with shaking at 37° C. for 2 hours. IPTG was thenadded to a final concentration of 0.2 mM and the tubes were shaken foradditional 5 to 6 hrs at 25° C. The cells were collected bycentrifugation and lysed chemically using the B-PER Reagent (Thermo).The suspensions were kept for 10 min at room temperature. The lysedsolution was designated as a “total cell lysate”. The “solublefractions” and “pellet fractions” were separated followingcentrifugation. The total cell extracts, soluble fractions, and pelletfractions were used for the detection of protein expression andsolubility, respectively.

Expression and Solubility Test

To evaluate protein expression and solubility, the total cell extract(T), soluble fraction (S), and pellet fraction (P) were separated bySDS-PAGE using NuPAGE 4-12% Bis-Tris Gels and the supplied reagents(Invitrogen). The proteins were transferred to PVDF membranes(Invitrogen) and probed with anti-His probe antibodies following astandard western blotting protocol. Following development, the proteingel blots were scanned with a flatbed scanner and the band intensity wascompared between soluble and pellet fractions NIH ImageJ software.

Results: Comparison of Solubility-Enhancement by Artificial EBDs

In order to compare solubility-enhancement by various EBDs, proteinsthat were known to be insoluble were cloned into the pAquoProt series ofexpression vectors and overexpressed in E. coli under a standard set ofconditions. The negative control for these experiments was the sametarget protein expressed from the unmodified AquoProt plasmid that didnot harbor an EBD but does translationally fuse an N-terminal His-tagand EK cleavage site to the target protein. The human metalloproteinaseinhibitor TIMP2 is an example of a protein that is entirely insolublewhen expressed in E. coli with an N-terminal His-tag (FIG. 8A). However,when 5 unique EBDs ranging in length from 24 to 250 amino acids areincluded in the fusion tag, a portion of the recombinant TIMP2 isdetectable in the soluble fraction (FIG. 8A). These results indicatethat EBDs can vary greatly in composition and length and still improvethe solubility of fusion partners. To evaluate the contribution of theprimary amino acid sequence and overall physical properties tosolubility enhancement, the TEV protease was expressed as a fusion to anN-terminal His-tag or three N-terminal EBDs that are composed of thesame four amino acids and have similar physical properties but differ inprimary amino acid sequence (Table 3). The solubility studiesdemonstrate that TEV protease solubility improves when fused to allthree EBDs with similar physical characteristics but distinct primarysequences are fused to the N-terminus (FIG. 8B). We also tested whetherfragments of longer EBDs could themselves be effective solubilizationagents. The human B cell activating factor (TNSF13b) was translationallyfused to an N terminal tag containing a 120 amino acid EBD and a tagcontaining a 60 amino acid fragment of the longer EBD. Both EBDsimproved the solubility of TNSF13b over the His-tag control construct(FIG. 8C). In some examples a single EBD fusion was insufficient todrastically improve the solubility of a partner. Therefore, the AquoKinexpression vector was prepared to facilitate the addition of EBD fusionto both termini of a target protein. To demonstrate the effectiveness ofthis strategy, the tyrosine kinase c-Src was expressed with anN-terminal His tag or 250 amino acid EBD (SeqID 15 (1-250). TheN-terminal EBD did improve c-Src solubility somewhat (FIG. 8D). However,when a second EBD (SeqID 15 (1-81)) was added to the C-terminus of c-Srcthe majority of the fusion protein was detected in the soluble fraction(FIG. 8D).

Conclusions

In summary, the translational fusion of negatively charged EBDs torecalcitrant proteins can dramatically improve solubility. Moreover, theEBDs are defined not by a specific amino acid sequence but instead bytheir physical properties. These results clearly demonstrate thatsynthetic polypeptides that are disordered and charged make foreffective EBDs. The EBDs can be synthesized, for example, by combiningdisorder-promoting amino acids in a large variety of amino acidcompositions and ratios. The variety of potential EBDs is furtherexpanded by specifically engineering variants to contain specificdesired features (e.g. hydrophobic pockets like those found in chaperoneproteins; SEQ ID NO 45). The effective length of EBDs is also not fixedas demonstrated by the fact that EBDs ranging in length from 24 to 250can be effectively employed. Adding EBDs to both termini of a targetprotein has also been shown to improve solubility over recombinantproteins that have a single fusion tag, demonstrating yet anothersolubilization strategy according to the present invention.

1. An isolated fusion polypeptide comprising at least one non-naturallyoccurring entropic bristle domain (EBD) as set forth in SEQ ID NOselected from the group consisting of SEQ ID NO: 41, SEQ ID NO: 42, SEQID NO: 43, SEQ ID NO: 45, or a fragment thereof, or a sequence having atleast 90% identity to SEQ ID NO: 41, SEQ ID NO: 42, SEQ ID NO: 43, orSEQ ID NO: 45, and at least one heterologous polypeptide sequence,wherein the fusion polypeptide comprising said EBD, or said fragmentthereof, or said sequence having 90% identity to SEQ ID NO: 41, SEQ IDNO: 42, SEQ ID NO: 43, or SEQ ID NO: 45 has increased solubilityrelative to the heterologous polypeptide sequence, reduced aggregationrelative to the heterologous polypeptide sequence and/or improvedfolding relative to the heterologous polypeptide sequence.
 2. The fusionpolypeptide of claim 1, wherein the EBD polypeptide sequence is about25-300 amino acids in length.
 3. The fusion polypeptide of claim 1,wherein the EBD polypeptide sequence is about 25-200 amino acids inlength.
 4. The fusion polypeptide of claim 1, wherein the EBDpolypeptide sequence is negatively charged and the amino acid residuesare disorder-promoting amino acid residues selected from P, Q, G and E.5. The fusion polypeptide of claim 4, wherein the disorder-promotingamino acid residues P, Q, G and E are present in about the followingamino acid ratios: E:P:Q:G=1:2:1:1, E:P:Q:G=1:4:1:1, E:P:Q:G=2:2:1:1,E:P:Q:G=3:2:1:1, E:P:Q:G=1:2:1:2, E:P:Q:G=2:2:1:2, E:P:Q:G=3:2:1:2,E:P:Q:G=4:2:1:2, or E:P:Q:G=5:2:1:2.
 6. The fusion polypeptide of claim1, wherein the EBD polypeptide sequence is negatively charged and theamino acid residues are disorder-promoting amino acid residues selectedfrom P, Q, S, G, D and E.
 7. The fusion polypeptide of claim 6, whereinthe disorder-promoting amino acid residues P, Q, S, G, D and E arepresent in about the following amino acid ratios:D:E:P:Q:S:G=1:2:3:1:2:1.
 8. The fusion polypeptide of claim 1, whereinthe fusion polypeptide further comprises a cleavable linker.
 9. Thefusion polypeptide of claim 1, wherein the EBD sequence is covalentlylinked to the heterologous polypeptide sequence at the N-terminus, theC-terminus, or at both the N-terminus and C-terminus, of theheterologous polypeptide sequence.